Itoya seems to be the book of choice.
I got mine from here:
http://www.darkharbor.com/trades/html/anime.html
Joe's a great guy with a terrific Ranma cel collection! ^_^
I've only one cel from the skating competition:
http://aernath.rubberslug.com/gallery/inv_info.asp?ItemID=100175
I was losing a bidding war for another skating competition cel when I came upon that one at a dealer's site. Grabbed it up quick! ~_^
Yep. They do tend to come in waves. Especially when you're trying hard to be good and not buy anything for a while.
That same seller just added a few more Ranma cels, and I just found myself snapping up a cute cheap Ranma.
He's adoreable, and I love him, but dang, I've been trying so hard to be good. ;_;
Welcome to the world of prioritizing and hoarding! XD