what exactly are you looking for?
just a piebald and you look for specific optics and nothing you can find is good enough?
or are you looking for a specific pied combo?
EDIT: also the breeders with the most advanced pied combos and the most pieds for sale will simply be the biggest breeders. breeders that have mostly pieds will most likely be small breeders. a big breeder may have 3000 BPs, of which 400 are pieds. you wont find anyone that has more pieds than that, but less BPs overall. but you may find a small breeder with 20 pieds and not much else.