I have one cel of Shuuichi currently in hand, and 
a second on the way. One came from a private 
owner, the second from YJ. Needless to say, 
neither's for sale. ^_^ I'm on the hunt for cels 
of K (!), Yuki, Hiroshi and Sakano to join him.

http://www.angrygamer.org/~titania/gravi.html

Your best bet is to find someone with good 
connections, haunt YJ, or be quick with a lot of 
money when American dealers get them.

Usagi's House still has 3 of Shuuichi in stock:

http://usagis-house.com/shopusagi/index.cgi?
ID=ZGOGK1&task=show&cat=Gravitation

Good luck!

A.