Besides Fehling themselves in Germany who have great links with photos and prices, I can find USA, UK, Eu and Australian retailers in minutes, most more expensive than Fehling direct but some hae good deals on items like Motea in UK who keep sending me 20-30% off email offers..
Despite having the Triumph factory rider's backrest with a custom solo bracket and all the dual seats that they fit too, I still have a new one of these in my shed along with quite a few other RIVCO Xmas tree style for Triumph Rocket IIIs; Corbin backrest stem attaching types; and a few factory and Mittzy made custom quick detach ones!