I am using a V brake and the light mount that I have in the photo was modified by me (I have a large vice, big wrench, big hammer, easily modified), so you won't find another light bracket like I have.

But I am showing the photo because instead of using a long bolt in my fork crown, I used a piece of M6 threaded rod and several nuts and washers. One of the nuts was taken from a brake pad so that I could use an allen wrench on that nut. I think I got the threaded M6 rod at a True Value hardware store. If your hardware store does not have metric threaded rod, quarter inch might work. But I like to use 100 percent metric on bikes so that I only need one set of tools.

The standard mount for the Luxos U is wire and I have seen photos of people wiring it so that the cantilever brake cable goes up through the mount. I was sure that Peter White had a photo of that on his website, but I just spent some time looking for the photo and I could not find it. I did a google search and found this link with a photo:
Dynamo Lighting - Need Help With Lights & Wiring

I think that is all you need.