I have made spacers out of wooden dowels (get one the right diameter, carve a small groove down on side and put a screw on each end with a wire in between). These are cheap and easy to make.
For something with a little more heft, use aluminum or copper dowels. Get one a little smaller in diameter, and apply several layers of heat shrink to bring it up to the right size (and to insulate it from the sides). These are more expensive to make, but are practically indestructable, and won't change the weight or balance of the light as much (like if you don't want to affect the boyancy of a modded dive light).
Aloha, iG