Cels Forum

You would be speaking of fan art cels, I believe.  There are
a handful of people who do this on commission listed on the
'Dealers II' page of the Internet Guide to Anime Cels:

http://www-scf.usc.edu/~ckawakam/cels/index-two.html

(just scroll down the page, the last tier is for fan cels,
including Moonshine.)

I've never bought a fan cel though, so I couldn't say who to
recommend.

Keys