As Daniel suggested buy from reputable breeder. With recessive genetics (most current python morphs are recessive) the only way to get 100% hets is to either prove them through breeding, or to breed a 100% het to the actual morph. For example, breeding an Albino to a 100% het Albino will produce Albino's and 100% hets.

http://www.geocities.com/bait4snake/genetics.html

Has some excellent genetics information, including what possibilities will exist when breeding different morphs. If you haven't read this already, make sure to read the section on Triple Hets. Get's pretty whacky at that point, and after years of breeding, imagine having an Albino Clown Piebald