Brahmas don't come in Partridge. There are Dark, Light, and Buff Brahmas.
Do you mean Dark Brahmas or perhaps you got them mixed with Cochins?
ETA: Ah, sorry for my ignorance. I looked them up and they do come in Partridge and Gold. Sorry, I don't know of anyone that has them. They are most likely a breed that is only in the UK for now.
There are a few breeders out there. I, myself have only seen pictures and no live birds. If you contact the American Brahma Club, you might be able to secure some names and phone numbers.
As for myself, I raise LF Darks and Bantams in Darks for the time being.