Hi, I have a 1968 124 Coupe and parts supply does not seem to be a problem. There are a number of specialists in the UK and Europe, check google for details.
The 124 Spyder is the same floorpan and shares the same mechanical systems. Also the 124 Sedan has many common parts.
Many Spyders were sold to the USA and there are still a few companies over there supplying parts.
Message me if you have any difficulty and I will see what I can locate.