It may just be my location, but for me they are pretty easy to find. I have noticed that they are pretty bad when it comes to hardiness, unless you have really good stock. I got 10 from a friend, I lost one randomly, not sure what happened, then lost another randomly. The 8 are holding steady and haven't got any diseases, despite having ick a couple weeks before getting them.
So maybe they die easily in new conditions and once settled they are hardy?