Go to the BikeINN website, I got mine from the warehouse in Spain. They really have a million parts.
I've been using bar mirrors that are like the ones on light motorcycles. They have an 8 mm shaft, so very steady as long as the pivot is still tight.
I did have to DIY fiddle a bracket from old shifter mounts.
They are absolutely perfect for me to see a long way back on the highway. Still OK in the city, but I use it less.