I have 1 or 2 rotating amber lights that mount on the roof of a car via
magnets and are powered by a 12v car plug. I bought these (and they
weren't cheap) for Emily O'Brien's riding of the Furnace Creek 508. If
you are planning on doing a ride with follow support (FC508, RAAM, etc)
and you need these I'll send them to you for the cost of postage. These
aren't fancy but Emily did win the FC508 twice and set a course record
so I think it's fair to say they did the job.
The only thing I'll ask is that should Emily rides another event that
requires follow support (unlikely, I hope) you lend them back to me if
they have not already been passed onto another worthy rider.
Jake