Check out the Mako tail light from Biltwell Inc.

Here's a look at our Mako tail light compared to a generic Sparto repop. The lens on ours is roughly the same size but the body is about 5/8 scale for a tidy look on just about any custom motorcycle. Note that you can sandwich our laser-cut license plate mount between the light and your fender. The Mako comes in black or polished aluminum for $119.95 and is available here.