If you want to buy from a California breeder you may want to contact the "grand dame" of Parti Colored Yorkies - Loryn Bogren at Crownridge Gems. Her website is not very up to date but you can see examples of her dogs there and find her contact information.
Parti Color Yorkies - Parti Color Yorkys - Party Color Yorkies She is also on Facebook.
Good luck in your puppy search. There are other good Parti breeders across the country if Loryn doesn't have what you are looking for.
Teresa