You can also check with Kustom Koach Works, Junction City, OR @ 541-501-3371, they do a ton of remodel work on Alpines so they most likely either have them or know where they can be gotten from. Normal stores won't have them like Home Depot or Lowe's. Speciality Cabinet shops might, but they are going to want some kind of ID stuff, i.e., model number, or style number. If you have those, you can try a search on the internet using that information.
Another option is to take one from a cabinet you don't open very often put it on the cabinet you do open a lot, and keep searching remembering that the cabinet needs one when you can find it.
Check with NW RV Supply, they might have some as well. They bought up a lot of parts from various places: Northwest RV Supply
Another source would be Aubrey's in Yakima, WA, see this link - http://aubreysrv.com/