I forgot to mention that the Cabriolet Club has also got reproductions of some of the hard to get parts for the Cabriolet for sale.
Then there is this gentleman in Denmark which has fabricated some sheet metal parts and patch panels for the Cabriolet :
http://www.poul-hedegaard.dk/index.htm
He definately has some offering for the 68-B. I cannot confirm for the 68-C, you will have to check.