I need to replace the plastic latch on a costco 02-480-WAL car seat. Is there a place to find replacement parts?

Junk yard. Google "junk yard" and your location and you should get some hits. Or I like car-part.com. Once you get them, you should be able to access the bolt that holds them in place by moving the seat all the way forward (assuming that we are talking about front seats). There should be a plastic cover that "pops" off with a little influence. Remove bolt, install new/used part.

There is a plug (cap) that goes into the pivot point of the release handle for the third row seats. If that plug is missing, you can stick a penny in there temporarily to enable the release and fold the seats down. The replacement part is called a "release handle plug" -- I found it at moparpartsovestock.com, part number 1ED82BD1AA for under $4.

Their website says to contact them about replacement parts. You can find their info here: Cosco

check to see if parts are jammed in the path of movement

Car seats are usually only good for 5 years unless there is a label on the seat that states otherwise.  you would be better off buying a new car seat

Vancouver-based manufacturer Stork Craft is voluntarily recalling more than a million baby cribs in Canada and the United States over a potential suffocation hazard.
The cribs were manufactured in Canada, China and Indonesia between May 2000 and November 2008, the company said in a release.
About 494,000 of the cribs were sold in Canada and 535,000 in the U.S. in several retailers such as Wal-Mart, Kmart and J.C. Penny, as well as on several websites, including Amazon.com, Babiesrus.com, Costco.com and Walmart.com, the U.S.Consumer Product Safety Commission said in an advisory Tuesday.
Apparently if you call them they may give you free replacements. Assuming the one you have is one of them.
I would try new/used stores,etc. if your's isn't one of the recalled ones.

you need new clips ,avable through subaru,i believe they are better than ones equipped originally

Do you mean the little straps that hold the front of the car seat in? On each side of the pushchair there's a short strap with a plastic thing at the end. These line up with the open-ended slots on the sides of the car seat. If you pull the strap straight, the plastic thing can just be tugged around the end of the slot on the seat so that the strap now goes through the slot and the plastic thing holds it on. It's tricky the first couple of times but gets easier. Sorry if that wasn't the question...

The door latch assembly comes as one piece. It would actually be much simpler to purchase the new latch and replace the whole assembly instead of trying to put pieces and parts back inside a latch that may or may not work after all your hard effort. If you decide to replace the latch, follow these steps: 1. Unplug the machine. 2. Remove the lower kick plate panel if you like (this can help you reach the latch from a couple of different angles). 3. Open door and feel around the rubber door boot for a wire hoop. At the bottom of the door open is a tension spring. Pull the spring apart and remove the wire hoop from the groove. 4. Gently lift the rubber boot from the groove around the door opening and push inside the machine so you can access the inside of the casing. 5. The door latch assembly is located inside the case on the right-hand side. There should be a couple of wire connectors going to it (remember how they come off). Be careful with the wires, they are small and can break. 6. Unplug the wire connectors and remove the three screws holding the latch in place from the outside of the casing. 7. There should also be a plastic retainer holding the latch in place. Remove latch from retainer. 8. Install new door latch by placing it in the plastic retainer, first. 9. Plug wires connectors in. 10. Re-install the three door latch screws. 11. Re-install rubber door boot around the door opening. Make sure it is properly seated in the groove. 12. Reinsert wire hoop. starting at the top of the door opening, carefully push the wire hoop into the groove and work your way all the way around the bottom where the tension spring would be. (A second set of hands to hold the wire hoop in replace would be handy at this point). 13. Pull tension spring apart and snap into groove. Done. Hopefully this will take care of your problems. Of course, you may not like the idea of having to purchase a whole new door latch assembly, or the effort required to remove and replace. But, it sure beats trying to rebuild the old one. I hope this helps.