A TMGC+C would probably be hard to find. The follow-up model, the Tamagotchi-iD has been out for almost a year.
Check Toys-R-Us, Bic Camera (in the toy section), Ito-Yokado, Aeon, and other large department stores that have a toy department.
If your friend is going to be in Toyko, then as black candy said, ask if they can pop into TamaDepa. TamaDepa will have the Tamagotchi-iD, and might even have a few TMGC+C.
Another suggestion: if your friend will be staying at the same address in Japan for more than a week, perhaps they could order one from an online shop such as Amazon.co.jp or even an auction site such as Yahoo Auctions.