These go through cycles of availability because there are few sources actually captive breeding them. The only one I know with certainty is "The Frog Ranch" and they do not make retail sales, only wholesale. Be patient and keep an eye on kingsnake and lllreptile - I see them there now and again.
They get between 3 and 5 inches long, depending on sex. That's about 7 - 13 cm.