The reason you don't see them is that they are extremely fragile and difficult to raise. Also, getting guppies and mollies to breed in the first place doesn't always work and they don't always produce viable fry. When they do, only a few survive and, the high mortality rate and the fact that they aren't realy all that special-looking means no LFS would stock them and no one would breed them on a commercial scale anyway. Also, considering lots of mollies (most actualy) and many fancy guppies are hybrids themselves, getting a hybrid molly to breed with a hybrid 'guppy' is even more difficult than it once would have been.