The bulb is not double sided, just the socket. I need to fit two bulbs on either side. I want to have a pair of 20w lights in the back, and a pair of 10w lights in the front for my 10g hex. The biggest hood that i could find that will fit over the tank is 36w, so i need to make my own.
I see, you mean you want to be able to fit two bulbs, one on each side.
It may be not easy to find the right spectrum, but check home depot for the screw-in type. They are replacement for regular incandescent bulb with a built-in (integrated) ballast.
If you have a LFS that sells Hagen stuff and you are on good terms with ask them to get them for you. They can order them out of the spare parts catalog.