If you need alot of cel bags, you can bid on 100 
ct cel bags on yahoo jp.  With the bid fee and 
shipping and everything else that goes with 
deputy service, alot of times....it's expensive, 
so combine shipping with other things you win.  
But if you need between 1 to 50 cel bags, you 
may want to ask www.anime-haven.net. They offer 
to the winners of their auctions, so just ask 
for some.  They have backboards for cels as 
well.  www.rinkya.com sells cel bags that aren't 
really cel bags.  More like plastic file 
holders, but they work.  Those are some options, 
hope this helps.