If you really want to breed snakes, I'd get another Texas Rat, whether it be leucistic, heterozygous, or plain old normal.
You could certainly try such a cross but there's nothing even remotely similar to it in the pet trade. At least that I know of.
The two species have historically been listed in the Genus Elaphe but they are really much more distantly related that that. Inter-generic hybrids have been produced, of course, but only among snakes that share a more recent common ancestor.
If you'll be disapointed if they don't breed then I'd buy another Texas Rat.