I purchased all of mine here:
http://www.nikaku.com/

The cel paints are listed in the "MISC" section, 
they have a very nice selection of genuine Toei 
cel paints.

I've used them to fix lines and missing 
correction layers on separate cel layers (you can 
purchase non-acidic acetate sheets at almost any 
art store), and I've found them to work really 
well.

For those of you local to San Jose, you can 
purchase them directly at the store (this is nice 
because you can see the colors in person):

615 North 6th Street
San Jose, CA 95112
Tel: (408) 971-2822 
Fax: (408) 971-0856   

Store Hours: 
CLOSED MONDAY
Tuesday - Saturday: 10:00am - 6:00pm
Sunday: 10:00am - 4:30pm 


-m ^_^