I'd look for a tungsten halogen (quartz) replacement. Off the top of my head I don't know what specific lamp would be suitable, but I'm sure you can find something. If not, post a note at controlbooth.com. I'm using halogen lamps in all of our old stage lights where I work and they work well. Light output from a tungsten halogen lamp will be superior to that of the incandescent lamps that you have now.

When looking for a comparable halogen lamp, compare the base (yours are either medium bi-pin or mogul bi-pin, I'm not quite sure), light center length (distance between filament and lamp base), and wattage (750W or less). I'm honestly not sure exactly how to measure light center length (LCL) on a bi-pin lamp, but donsbulbs probably explains it. Hope that helps!