Cycle treads on the shore do the small 23watt 12volt bulbs as they suit the emgo lamps about $17 for box of 10
most of my auto sparky trade suppliers dont do bike stuff they say there's not enough money in it, not suprised at that price
as for the 6 volt bulbs, try some of the scooter shops alot of them run 6 volt systems
cheers scotty