You could check BirdBreeders at:
BirdBreeders.com - Bird Breeders Directory of Availability and Parrot Breeders . It is a site of breeders from across the country. The mutation that you are looking for is hard to find around here, or at least it used to be. You should be able to find quite a few breeders. If none of them breed that mutation then they might be able to put you in touch with a breeder who does. Good luck!
Matt