QBP Problem Solvers Brake stud Mount LT0901
+ the afore-mentioned Schmidt Part#: SCH75532 handlebar mount gripping around it. perhaps ?

I use the ' Schmidt headlight mount for Brompton fork crown, stainless:' in mounting an Eyc on my Brompton.

you could fabricate something yourself [bend a L bracket with a hole, each, for 2 bolts] ..
But this forum seems to prefer seeing shopping links..

People get Surly Bikes over there so there must be a QBP distributing importer to Europe.

here's German B&M via UK http://www.sjscycles.co.uk/busch-and...33640/?geoc=us

http://www.sjscycles.co.uk/schmidt-h...23929/?geoc=us