Pet stores have them, including most of the online bird supply sites. I just bought a bulb from one of those and put it in a regular lamp -- well, it's a clip on garage light! -- rather than spend $30 for a special lamp. It's hanging between the two cages and pointed so it's not glaring right into their eyes but casts light over them and we have a house plant on a shelf above them that's thriving thanks to the light.

You should see how spectacular Clyde's tail has become since we got that light. It wasn't that long and pretty even last summer when he was going outside regularly in his cage and spending afternoons on the deck with us.