As said before, LEDs are Light Emitting Diodes. They allow current to flow one way (unless you exceed the reverse breakdown voltage, then they go POP). LEDs typically turn on when they are exposed to 1.7 volts (across the terminals of ONE Led), which we normally round up to 2 volts for most circuits. If you know that, then you know that the maximum number of LEDs in a 6 volt system would be 3 in a series configuration. In a parallel configuration, you can add togther a number of 3 LED strings to get the amount of LEDs that you want - they will just consume more current than a single string (but likely less than a normal 6 volt bulb).
What you need to find is a company that is making LED lights with 3 LEDs in a string. Most companies will tend to make 6 LED strings (12v) because of the 12 volt standard.
It COULD be possible to convert a 12 volt LED light to a 6 volt light, provided that the circuit bord isn't potted in a plastic resin (to prevent you from gaining access to the circuit wiring). You would cut the 6 LED strings into 3 LED strings, and move the power and ground leads appropriately.
