Hi used to order third party help buying cels 
from Japan from a fellow I knew named Toru from 
Anime-Cel Depot.jp, a Cel Store and auction 
house called Mandrake and another named Anime-
Taro but I've lost contact with all of them some 
time ago. ----If anyone knows how to reach them 
send me a reply ^_^ ---- 

I know www.Celga.com (Heigo is his name I think)
and www.Rinkya.com would be able to give you a 
list of Cel Stores in Japan as they work with 
them directly and frequently.  You can also try 
http://www.takamura-store.com/v3/en/ as they are 
a cel store in Japan whom I believe are very 
familiar with the cel scene over there.

Good luck!
     John