You can find them at most cel stores in Japan.  I 
usually get them at Anime World Star.  They have 
I think A-4 and B-4 size bags.  A-4 that holds 
normal size celswith sketch at 800 yen per 100, 
and the B-4 which holds most cels with 
backgrounds at 1000yen per 100.  Yes, they hve 
the sticky strip.  They are very clear, and thin 
compared to other bags I get.

RX78GP02AGUNDAM