Divers den has them on occasion. NYaquatic has one listed. Pieces of the ocean and zoa collector are two others worth checking out. I don't have any personal experience with any of these vendors except for DD.
Sometimes you'll find one at your LFS, and then you can watch it move in the tank or even feed. That can make a big difference sometimes.
That having been said, Michael at NYAquatic (a Reef2Reef Sponsor!) is a terrific fellow, and states on his site that he won't sell a regal that isn't feeding.