Go to
www.yorkiefantasy.com. Diane makes yorkie clothes and I believe she also makes custom sized belly bands. She's a member of my group, littleyorkielove, and I just bought the cutest little outfits for my two boys from her. She does excellent work. Also, I belong to YorkshireTerrierBoutique, and I am sure someone there makes them, if Diane doesn't.
http://groups.yahoo.com/group/yorkshireterrierboutique.