The Thayeri and Mexicana above may not be pure. If you want either of those species and you want a pureblooded animal be sure to get one from a breeder that is really anal about locality snakes. There has been a LOT of mixing in those species in the last 20 years.
My Thayeri (posted early in the thread) is definitely pretty darn pure. He's from Vivid/Vermilya lines. But that's a good point and it's not just limited to L. mexicana.