Thanks kabuto and sweeks. I was looking for a spare "hanger" since I did not want to go on an 800km tour and damage the connection between frame and derailleur without having a replacement. It looks like my only option, in the event of an accident, would be to buy a new derailleur. With a Tern in the middle of nowhere this could take a month. It looks like I need to take the risk that the "hanger" will not get damaged.