There are various owner's groups/forums which can help locate the 'bit' you need as well as the regular 'auto jumbles'. Newark is a good source of both pattern and OEm parts for 70s & 80s japanese bikes (as well as most 'Brits'). Unless it is a complex part (i.e. carb) then most times you can 'adapt and fit'. This includes fuel tanks, lights and suspension. Just 1 word of warning - You are very unlikely to make any profit from a rebuild unless it is a very rare and sought after machine. Plus 'Barn Finds' are not usually actual 'finds' at all! I have been 'rebuilding' a 1974 MZ for a few years now and it is at the 'roadworthy' state - Spend to date is approximately £350. Bike value is approximately £300.