I don't have any idea who sells them but from what I gather they are becoming more popular as pets these days.
Are you able to go to any reptile shows? Maybe someone at a show would have some for sale.
I've seen more & more ads for them in the back of Reptiles magazine which BTW has their "All Turtle" September issue out in the news stands now.
As for the ads in the back of the mag, I wouldn't have a clue who is reputable & who isn't but you might check the Breeders/ Dealers/Stores link here at the top of the page on Kingsnake.
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PHRatz