Personally, I prefer something like a Surefire Z2 led with a speed ring, coupled with a V70 holster. Something just seems wrong with a flashlight attached to a revolver.
Yeah, S&W makes a revolver with a rail on it.
It's marketed for swat teams to use as a "shield gun"
It's another answer to a question that NOBODY ASKED!
Now I can see it as a house gun, but still it's an awful lot of money for something that sits in a nightstand.
Man, I have foggy memories as a kid of seeing lights cobbled to revolvers in the last 70s and early 80s however I think that may have been a dry firing system. Back then flashlights were massive things.
This is the only thing that I know of. The website says it works on semi-autos and revolvers. Although, I've never used it so I'm not sure how well it works.