Not too long ago, it was actually fairly easy to find a lot of non-photo corals at LFS and online. I remember seeing a lot more available when I first started. It seems that their reputation for being extremely hard to keep in the average tank decreased the demand for these corals. This is a good thing.
As far as online sources, I'm not aware of any particular site that has carries a wide variety of non-photo stuff. Usually, you just have to scour around until you find something. Thatfishplace has a few things that I have not seen elsewhere, including Stylaster sp. fire corals and a number of different tunicates, but I have no clue as to the quality of their livestock.