The two big ones are the Safariland Comp III, and the Jet Loader. The Jet loader seems to me to be a little better built, and I have several of both.
Check this link for the best deal on a Jet Loader.
Revolver / Single Action : GrandMasters L.L.C., Gunsmithing, Ruger 10-22, AK-47, Ruger, AR-15, Ruger Accessories, Gunsmithing Tools and Gun Accessories
Power Custom has the best price I have found on Jet Loaders. Look down at the bottom of the page.
The Jet Loader is an even better choice when using a K Frame. They are smaller in diameter than a K Frame Comp III.
You need kydex belt carriers for them also.
Bob