As I bet you know, 3651W1A022B is the correct original part number for Kenmore (by LG) model 721.80019401 and as I'm sure you know, it has been discontinued, with no other substitutes listed.
You could take the old one and *some* appliance shops will try to visually match it for you to see if it would mount, even if the color or style is different.
You may be able to find an original in "new old stock" at some parts supplier, either locally or online. I would Google the part number, then call them and ask if the part is actually in stock on their shelves.
Some suppliers list them on their Web site, even though they would have to order them, and sometimes you wouldn't be told it is "No Longer Available" until some time after you have placed the order thinking it was available.
Or you may be able to fix yours. I would first wash the broken handle in a dishwasher, then only dry it with compressed air or let it air dry.
Then I would use JB Weld (or something similar) to pack into the broken end. Once it's dry, I would sand it as needed, then drill a new mounting hole for the screw.
Let me know at microwavecontrol.com
if I can help further.