Mangaya has a couple...but the prices are pretty 
obscene ;_; Like Sheri said, they're *really* 
hard to come by, so don't feel too bad. Take, for 
example, this conversation between yours truly 
and a cel dealer in Tokyo:

Amber (in broken Japanese): "Do you have any YYH 
cels? I'm especially looking for Hiei and Kurama."

Cel Dealer-san: "Do *you* have any? I'd be 
willing to give you a nice deal for them!"

You get the picture :)
Just keep checking the updates, and I'm sure 
you'll come by one! Good luck!!