I have a used Magura HS11 hydraulic rim brake that I no longer use.
It has a broken part (evolution adaptor) that can easily be replaced. I have received a quote (AUS$63 including delivery) but as I seldom unicycle at the moment I have decided to get rid of the brakes ‘as is’ rather than fix it. I figure that it would be better off being used rather than sitting in a box in my shed.