Apparently, they're not all that common and not always easy for folks to find, because there are always people here asking for them.
I can buy a halfmoon at a petstore too. It will probably be sickly and will definitely have no known background, which is why most folks don't get the pet-store ones, they buy from a breeder.
I bet if some breeders took them seriously enough to breed nice ones, they'd find out there IS a market.
Not sure what the real reason is, but I wish I could find some nice ones, too.