Check out ebay for International sellers. I remember seeing some shifters and parts in France and Germany a while back. The prices and freight seemed pretty reasonable too.
I bought a Duomatic (probably from the same seller), and it's great. I've put a lot of miles on mine, so I pulled it down for a service a couple of weeks ago.......shouldn't have wasted my time, all I ended up doing was repacking the outer bearings, but they would have been fine as they were.