I have looked far and wide. Even found a set to buy....of 3(!!), and I'm very reluctant owing to the unknown provenance and obvious difficulty securing a fourth. Any insight is very appreciated.

 

Inside the wheel there are normally manufacturer’s marks and or part numbers. Often the marks are small and require close inspection. This can help indicate whether it was a factory option wheel. Carmakers don’t manufacture wheels in house.

 

Lower right hand corner; Grid markings?

 

The mark on the lower left is Japan Light Wheel Alloy, required for Japanese markets. What else do you see on the other spokes? Can you post clear, close photos?