In my opinion I would rather seek a private breeder. Petstores do have a nice variety yes but then again if you find a reputable breeder you can can basically the same snakes and sometimes for half the price than what the petstores sell theirs for. Well this is the experience I've come to know after purchasing a handful of snakes. For instance a butter corn I bought for R450 I could have bought from a breeder at about R150. You do the math
What has already been mentioned is checking classifieds, usually gumtree and junkmail have a load of snakes on them plus you are able to find breeders pretty quickly. This is the step I've taken to get new pets and seems a lot lighter on the pocket if you have patience checking the net out.