Only place that makes them is Ruf. It is part of their RGT package.
A few years back I bought the complete RGT body kit (Less the Black Wing) for a customer, but it was never installed. Still have it as NOS, but don't want to break up the package just for an experiment.
The duck tail described in my first post I bought used, and will try to fit it to the C4S.
I will post the results.
Len