Does Andy grow his own stock? If so a lot of the rare cultivars are rare because they are difficult to propagate and aren't fast growers. It may seem like it's very obvious, but a very true statement. They may not appeal to a large number of specialized growers too but the regular joes are not going to care about rare and difficult cultivar. Not too many people are willing to plop $40 on a D. graomogolensis when they can get a capensis for a few dollars.