You should be able to find polished aluminum reflectors at most of the online places like That Fish Place, Big Al's or most any of the specialty marine places.
Before I got my Aqualights I was running three 30W T-12 bulbs in the hood over my 40g. They were mounted over a single 8" wide polished aluminum reflector using bulb clips screwed through the reflector. Not the most efficient lighting, but it worked better than white paint.
But I would recommend that you use a separate reflector for each bulb as this will minimize your light loss due to restrike.
I use the reflectors that came with the original All-Glass fixture but you can use just about anything. Hellolights.com is currently selling two reflectors at clearence prices, I just ordered a couple for myself: