I got REAL lucky on EBay several years ago. My 560SL didn't have any visors when I got it - no mounting bars, just holes where they went and the plastic female end clips in the windshield header. One fine day I browsed and found a pair in grey, in perfect shape, mirrors and all, complete, for just over $200.00 buy-it-now. Boy, did I jump on that fast. If you persist, eventually a pair will appear, but much easier to find if you only need the flaps.
Before I found them, I looked at retrofitting a pair from another model. It should be possible to do this, IMO, but only if you have the mounting hardware parts. I did search and found several articles on refinishing these, basically similar in design of the vinyl flap part.

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1986 560SL
2002 Toyota Camry
1993 Lexus