Velogical Engineering of Germany have hit the market with a very
small and light siderunner that is designed to run on the rim, and
may be an option for unicycles.
It puts out 6V/3W electricity (as is standard for dynamo lighting).
The website is still in German only, but worth looking at for the photos.
Note how unexposed it can be mounted with the o-ring mount.
150€ + shipping if bought directly.
I’m considering to get one, but not for the uni.
If I do, I’ll report of course.