The episode 2 ova cel was from Anime Taro.

So far, I've gotten my Ryoko (& Oryo-San) cels 
from Art Shop Rose, Anime World Star via Celga, 
Yahoo Japan, Animegame.com, Micke's cel shop, 
Anime Taro, eBay, Celmart, Yahoo US, Bonbee, and 
Anime Gambit.

Regarding Yahoo Auctions (US), nobody sells cels 
on there anymore, with the exception of oion's 
auctions and that $1000 DBZ auction.  (I believe 
oion has 2 Ryoko's for sale.)