Have you tried GPS Warehouse they carry a good range of Ram Mount gear.
Sorry forgot to include - http://www.gpsw.co.uk/results.html - 309 items listed but no sign of the brake mount. I would think they could obtain the part you want if you contact them but if you have a good look through you could just find a cheaper answer to your problem.
A forum community dedicated to BMW Luxury Touring motorcycle owners and enthusiasts. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, reviews, and more!