Scott: You have hit upon a big gap in the market. I have often thought of how this is needed, particularly for use on a .44 magnum revolver in grizzly country. If a bear decides to come through the wall of the tent at 3:00 AM, I want to grab something that will give me both light and a weapon.
The same principle applies for home defense. I use a USP .45 with the tac light attached, and it is a great setup. It is far handier than trying to juggle a gun in one hand and a light in the other.
Unfortunately, I don't know of any current revolver/light setups available. I have had the idea that you could have a full underlug drilled to accept a male Weaver scope base, which would allow a 1" light such as the Surefire to be mounted under the barrel in a scope ring. You could then detach the light and leave only the scope mount base on the gun. This would interfere with holstering, however.
Maybe some enterprising soul will read this and design a quick-detachable light mount for wheelguns.
Good Shooting,
CoyDog