Food sticks to griddle - Coleman Roadtrip Grill LXE 9949-750

I don't know but i need one too!

Yes, Lodge made a nice 20 inch cast iron griddle has bigger surface to cook more food with two side handles to make it easy to move. You have some other options like Presto 22 inch griddle, check out this link for different size griddles and pans with detailed information.
GroomNStyle Top 5 Best Saucepan and Pot reviews 2015

I have the same thing happening with my Viking griddle. I have nearly the whole top seasoned to a jet-black state - and it is stick free!! Now up near the front edge the coating/seasoning is chipping off. I've just been taking the loose chips off and not worrying about it too much, it maybe the size of a half dollar at this point. The front edge of the griddle is the hot spot on mine; and I've learned to adapt my cooking techniques. My guess is the hot spot on my griddle is responsible for the flaking...

well this is different, but sounds like fun. I would just Repair the gas griddle you have. from the sound of it you need to replace the 3 or 4 tstats that control the griddle. If you are in a Metro area you can find a dealer for Robert Shaw and get the parts you need. but you may also start at http://www.garland-group.com/. everything there will be newer but you will be able ask about where the data plate is and then get parts lists. call a small comercial kitchen repair company and ask for help there too.

I can't help you with the manual because you did not provide the make and model number.

Typically, you wash the griddle with soap and water (DO NOT WASH ANY ELECTRICAL CONTROL UNIT!). Rinse and let dry if it has a non-stick coating. If it does not have a non-stick coating (bare metal), towel-dry the griddle, then put some vegetable oil on a paper towel and wipe the entire cooking surface so it is covered with a thin film of oil. Heat it to about 250 °F for about one on-off cycle on the electrical control. It is now "seasoned" and ready for use. If the griddle does not have an electric heater but is designed for use on a range-top burner, set the burner to just below medium heat and heat until water droplets splattered on the griddle boil off quickly.

This range has a standing pilot light for the top burners and griddle top. If you look through the small hole under the flat top griddle you can see a small line about 1/4 inch that runs from the main gas manifold to the pilot light about 6 inches back under the griddle top. You will need a tightly wrapped piece of paper or a long match or small wooden stick, like a chop stick. Light the end of your paper, or stick and put it through the hole all the way to the pilot light. It should catch on fire. Whenever the main gas line is on, the gas will flow through the pilot light. If it will not light, there is a pilot light adjustment that is a very small screw in the middle of a 1/2 inch square metal fitting that is screwed into the gas manifold. If the pilot won't light, this screw may be turned all the way in, thus cutting the gas off to the pilot light. If necessary take a very small flat blade screw driver and turn the screw counterclockwise a half turn. That will increase the gas flow to the pilot light. Another way to light the pilot is to put your burning stick or match into the hole near the burner under the griddle plate, then slowly turn the heat valve to the on position. The main burner will light and then the pilot will light off of it. Don't get your face too close to the griddle when you light it, gas can flash back into your face.

This is taken verbatim from page 11 of my Frigidaire Gallery range:
"Seasoning, using and caring for the griddle Before first use: -Wash griddle in hot soapy water. Rinse and dry completely. -Apply a thin coat of vegetable oil to the entire surface (front and back of griddle). -Preheat your oven to 350*F. Place the griddle on the upper rack in your oven. -Bake griddle for 1 hour at 350*F, then turn oven OFF and let cool before removing. -The surface may have a tacky feel to it from the seasoning process. If desired, wash the griddle in hot soapy water, rinse well, and dry completely.
Using the griddle: Remove the center burner grate and carefully replace with the griddle (some models). Preheat the griddle for 5 minutes on medium to medium low setting. Slow preheat ensures even heat distribution during the cooking process. DO NOT preheat the griddle on HI setting. Preheating on HI may warp the griddle and prevent even heat distribution.
After each use: -To prevent rusting, store in a dry place and keep uncovered. -After each use, clean with a stiff brush and hot water only. -Do not clean griddle in the dishwasher. -Dry immediately and apply a light coating of vegetable oil to griddle before storing.

part number for the griddle is WB31K10140
partstore.com has it for $87.95 hope it helps

This addresses the cleaning question only. I was a chef for 27 yrs.  Once the griddle surface has begun to rust, and this can and even will be the case on a new stove, you have to get agressive with it. You're going to use sanding tools and oil. 
If the griddle top is heavily rusted, I use my electric palm sander fitted with fine emory paper (the black stuff that can get wet). Wet down the surface with a small amount of oil and work the sander evenly over the entire surface in rhythmic strokes from front to back or side to side. I don't have a scientific reason for this but my gut tells me not to work in circles or random strokes. Try to work the entire surface evenly to avoid creating high or low spots. Use a straight edged spatula or I use a dough cutter (flat edge of about 4" and available from culinary store for under $10) to cleanly scrape  the dirty oil off the surface. Sand in shorter durations & clean often to avoid grinding dirty flavor into the surface. 
Once you have it clean its time to season it. With a better oil focusing on flavor, spread a thin layer over the surface and cook at about 250 degrees for 15 - 20 minutes. Repeat this after every use until you build up a layer of cooked oil almost like enamel to resist rust between uses. This makes a teflon like finish to your griddle.
For regular use and cleaning scrape down immediately after cooking and while the griddle is still hot. When its cool use a hand sanding block you can get from the hardware store. The one I prefer is a firm sponge with emory paper wrapped around it. I store this in a bowl on the shelf above the stove because it is oily and dirty. Alternately you can also use rock salt and a kitchen rag to loosen food particles stuck to the griddle but this makes for messy laundry or throw away rags. We also use viengar or lemon juice and water to loosen food while the griddle is still hot or warm. NEVER USE SOAP!!!!!! You want your food to taste good don't you?
The oil used for cleaning can be anything with minimal flavor like canola oil but the oil used for seasoning the griddle should be a high heat type like sunflower.
Personally I only cook in black cast iron pans and the above method is how I treat them as well. Rock salt and water is all I ever need to clean them between uses.
Rick Casey

Hi there!

When it is warm, use a spray cleaner and paper towel to wipe up the grease.
Wooden or non-stick spatulas make excellent scraping tools to take the worst off first.

Use paper towel to wipe up.

For really stubborn deposits, use an oven cleaner - and cover with plastic film. Check in 1 hour, and clean as above.

Soda Crystals dissolved in hot water are excellent at cutting through grease, but may affect aluminium. They work out cheaper than many commercial products.

Hope this helps you.