Just one of a variety of possibilities can be seen below in the link below. Although not designed to be a quick draw holster, it's very secure and adjustable.
Check here:
http://www.maxpedition.com/store/pc/UFBS-9p238.htm
It's adjustable to accommodate a variety of medium to large headed lights, it's extremely durable, can be worn vertically, horizontally, and in a variety of other positions with Tac Ties or other straps. I use them with a Malkoff HD & WC, and a Tiablo A10. The top strap can also be adjusted for the size of a specific light's head, or it can be tucked back behind the light's head, or removed altogether for quick access.
The UBFS can be found here at one the lowest prices:
http://www.batteryjunction.com/maunflbash17.html
Good luck!