If you have any trouble finding someone to sell ya one, here is a place that sells the 10,000 RPM motors for the BitCharG 1/64 scale cars ->
http://www.animenmore.com/gs02.shtml . I'm not 100% sure if the BitCharG motors will work properly in a ZipZaps car (maybe someone could jump in here with a reply), and their prices seem quite outrageous ($6.99 for the motor!... dunno how much that their shipping is), but it may be the only source (if you can't find someone to sell ya one), other than on E-Bay.
I myself only have one of them, and to quote an edited version of a popular firearm owner blurb "I'll give up my 10,000 RPM blue motor when they pry my cold dead fingers off of it" <LOL>! -