I'm not really sure where to tell you to look 
except perhaps YahooJapan, Mandarake or I think 
AnimeChaos actually has a section for original 
art.  I bought a page used in the production of 
vol. 3 of Kamikaze Kaitou Jeanne on YJ a few 
months ago...(it's a publishing page, not hand 
drawn by A. Tanemura, but still friggin' cool)