Bulbs for Auxillary headlights on motorbike

[EMPOWERTORCH]

The ravages of poor road surfaces and speed humps have taken it out on my Lifan's headlight bulbs. The main bulb has already been replaced and one of the auxillary bulbs has failed. The main bulb was reasonably easy to get hold of, but the auxillary bulb is an unusual fitting, a single filament "miniature pre-focus" 15W halogen bulb. Any suggestions on where to get a replacement, or would it be possible to upgrade the base with a SE white Luxeon which would be much more resillient?

[EMPOWERTORCH]

I've been to every bike shop in town including the Lifan dealer and they all drew a blank. Plenty of double filament bulbs with the same base, but not a single filament one.
These are suggestiomns made by some of the bike shop proprietors.
1. Use a 6V dual filament bulb in place of the 12V single filament bulb. As the two filaments are connected in series and are of the same wattage, so the bulb will effectively light up as a single filament 12V bulb.
2. Rewire the spotlamps to take dual filament bulbs and arrange for all three lights to work in unison with all three lights being capable of dipping. A switch in the spotlamp supply could enable just he headlight to operate on its own. The total headlight wattage would be 75W, exacxtly half of the 150W available. Changing the instrument panel lamps to LED, as well as the turn indicators and the back light should help me conserve watts and will lead to improved reliability.