I'm afraid, the bulb holders are no longer available s I tried to source them a while back. They hold 12 volt 194/BP2 bulbs. They have bendable wire loops that make the contact with the bulb holders. Problem with mine were they were stretched and when I tried to tighten them, the broke (or at least 2 diametrically opposed contacts did). I solved the problem by bending one loop over to the other side so they made the appropriate contact. By the way, if you find a source for them, please let us know!
Thanks in advance.