Here is one type to look at. The bracket I think you can order separate if you already have the light.
There are tons of ways to do this, running the wires has always been the thing I consider weather barrel or scope mounted. I have seen set ups were there are hardly any wires to get in the way. They ran the wiring in the gun stock.
Coon Hunters Favorite ~ Model No. 1083
This pack age includes Nite Lite's THE HEAD. The headpiece clips off the hardhat for hand spotting, clips onto your battery for a hands free walking light or onto your rifle barrel with the barrel clip for easy night hunting. This Package also includes the rheostat switch cover which lets you adjust your light from a dim eye finding light to a super bright spotlight saving bulb life. The cover has a plug-in jack for recharging that plugs from the battery right into your wall outlet. The power source is the lightweight Gell-Gell rechargeable Nite Lite battery
with molded belt loops and weights only 3 lbs 14 oz. This package gives you hours of hunting light and is rechargeable hundreds of time. Battery is completely leak and spill proof.
Package includes: The Head light, Gell-Gell battery, Rheostat switch cover, and barrel clip.
Model No. 1083 ~ $104.95