Thank goodness there are more of us these days.  
*grin*

As to purchasing art, Anime Museum is indeed 
your best bet.  While I've seen a bare handful 
of production sketches sell on Mandarake and 
Yahoo Japan, the ending prices were painfully 
high.  And the few you might find on eBay from 
time to time all came from AM to start with, heh.

In the non-dealer side of things, though, I know 
that Agent_of_Solaris has at least a few lovely 
genga to trade or sell (check his post above).  
I believe Star Phoenix might have some as well, 
if I'm remembering an older post correctly.  I 
only have one up for sale right now, of Mamoru 
pleading with Ayato (check my website's sale 
page for image).

One way or the other, though, welcome to fandom 
of the show, and best of luck in your search for 
art!  ^__^