There are at least four, that I know of, the Three full framers, I think S&W, Ruger, and Taurus all put them out, but I might be wrong about the S&W and the Taurus, I know there are three of them at least...there is also at least one pocket pistol out there, a little 4.5" bbl 5 shot-I don't know who makes it or what they cost, I've just looked at them curiously in the gun shops, and I've seen them used in the field, a couple buddies and I go coyote hunting on horseback, they use these pistols for shooting them, I've seen them used out to about 100yrds with great success, off a standing horse free 2-hand saddle-seated shooting, making headshots mostly.

Ruger puts them out in the single six, I think only in the adjustable sight version though. The other two are kind of over sized for my liking, but they'd likely be better for varminting than the single six, although like I said, the simple little pocket pistol revolver did quite well, the single six would be much much better, and the two light target pistols would be probably fairly better still.