I've had more luck finding Transformers cels on 
non-anime cel sites (i.e. animation galleries 
which specialize in American animation.)  A 
number pop up on eBay from time to time, as well.
I've got a few cels from the Japanese Beast Wars 
(Neo & BWII) for sale, if you might be 
interested.  A while they're not for sale, I've 
got a few G1 Transformers cels in my gallery, if 
you want to take a look. ^^

~Mala