Thanks Michel, John D, John H.,

Considering all your advice, I think Michel's 'POM' would be the best way. Those pull switch knobs and rheostat rings that Michel had made looked spot on.

I'm only asking because I now have two original Fiat Dino Coupe full diameter (front) black window knobs, but with a spare pair of the chrome wingnuts.
The spare wingnuts need somewhere to live. I think making just one cloned pair of the black plastic parts isn't going to be possible.

Production of the black plastic parts would also need production of the chrome parts. I really don't think there are enough Stratos rep. builders/owners who care enough about this level of authenticity, to make it viable.