I think the main reasons for some types not being commonly available is a combination of them having a limited range and there being a limited number of people who take interest in them. For a species to get into circulation, there would have to be someone actually within their range that takes interest in them and legally collects and distributes those to that very limited group of people who take interest in them. I own a 2009 pair of santa cruz... some infernalis, eastern blacknecks, oregon red spots, and many others, and as for sierra garters, if I come across some I will get some, but I probably won't go out of my way for them because they are just not as attractive as most of the snakes I already own.