Do you know the names of the studs parents by chance? You might want to contact Walker's West. Walkers West - Tennessee Walking Horse breeders and brokers, world-wide.
They deal alot with spotted saddle horses and they have references to two stallions
Cotton's Power Kitty and Dot's Shamrock. There might be a connection and there might not be but its worth a try. You can also try All Breed Data base. If this horse is in the data base they sometimes have photos of them. If not your out of luck.
You can contact the registration office that the stud was registered under sometimes they have photographs on file for identification of such.