Try Donsbulbs.com and PAR36 Aviation spotlight. And have $42.00 handy. Instead of rubber try a metal headlight mount. This bulb is a VNSP, Very Narrow Spot Light. A little black metal cap shields the front half of the filament so the light emitted to the rear reflects off of the PARabolic mirror generating a very tight beam. I had stop signs a quarter mile ahead becoming visible. The lamp is designed for 13 volts and to last a few hundred hours. A 12 volt battery will make it last a lot longer. I would use Hawker(Gates) Cyclon J-cells and 12 guage wire.

100 WATT BIKE LIGHT. RIDING WITH POWER!