Ideal would be if you live in driving distance to a good breeder. My second choice would be having one shipped from a good breeder.
I don't recommend buying from a petstore at all, and you also have to be careful at expos, make sure you purchase from a reputable breeder. Sanitize your hands between handling of different snakes. Change clothes after coming home, and wash them. To make sure you don't bring home any hitchhiker snake mites !
There are also some members on this forum who breed snakes. Perhaps you are located near one of them ..