First a quick question: do you ever intend to use that canti boss for a brake?

I ask because they are very easy to permanently damage by applying too much torque to the bolt that is normally used to secure the brake. I have a B&M Cyo lamp and it requires a respectable amount of torque to the mounting bolt to keep it stable, but mine is mounted normally to the fork crown.

Also, I think you can get the knob and handlebar mount in Europe since I think Peter imports them anyway, though I'm of no use to suggest any retailers.