**broken link removed**
These are cheap plastic ones but look like they would work much better for your application than a metallic reflector, the plastic will glow so the headlights will look VERY bright, obviously it won't project light as well as a metallic reflector would but if you're actually trying to use this for external lighting on an RC car to drive it something is obviously wrong, it's for flash and appearance not actual light projection.
A simple Google search will net you dozens of links.
You could probably home brew your own diffuse reflectors like this out of cheap plastic.