Based on logo the owner belongs to the Eisenhund Kameradschaft (Iron Dog Camaraderie), I would try to write them directly.
Eisenhund Kameradschaft, Deutschland - Die Triumph Rocket 3 Fan Community - Eisenhund Gemeinschaft here is the contact form:
Eisenhund Kameradschaft, Deutschland - Die Triumph Rocket 3 Fan Community - Über das Kontaktformular
Also I think Hexenwerk guy is registered here on the forum, he is from Germany, I would shoot him private message, it is a some chance he knows the guy or how to contact him.
Also, few interesting "Lenkerumbauten"
from german R3 forum. Google can translate for you..
www.rocket3.de • Anmelden
May also be something from TRW catalog, page 5.25 and on
http://www.trwmoto.com/Global/downloads/Motorrad Kataloge/TRW Katalog 2015_low.pdf These have TUV certificates and many german bikers do not challenge the regulations as their regular inspections are detailed and include aftermarket parts mounted on bikes.
edit: looks like you would need to be registered on rocket3.de, so here are few pictures. Hope I am not breaking some rules: