Soo... lets assume you already have a fixture you want to 'air cool'. One of the interesting things I found in 'Barrel of green' posted by Major Toke and By Dr. Pot in this forum was the way they made the light easy to ventilate. They used a round clear plastic tube that is sold for baking bread. Readily available at stores in your neighbor hood, and if anyone sees you buying it they will like you.
Mogie did a post on installing a glass shield for a light that doesn't have one. You may want to check that out, an enclosed unit can be air cooled efficiently. I would think any Hydro shop will carry flexible ducting that will 'with stand the heat', VV