Well, I buy my cels from Pearls art supply stores.
However, those are only in the South East^^;;
Is Culve City anywhere near LA? If so, you may 
wanna check out Cartoon Color! They cel
animation supplies. (It's a cute pun^^;;)

If that doesn't pan out, call some of the bigger 
art supply stores where you are. The cels come
in packs. Blank production cels come in packs
as small as 100. You can get other types
of acetate in smaller (less expensive) packs. 
Talk with someone in the paper dept. They should
be able to help you out. Just make sure you get
something acid free that can take markers, pens,
ink. Stuff like that.

 Hope this helps!
-Amy