Welcome to the board. Poland ! That can't be easy doing an old American car there.
It's hard here in the US to get the old colors matched, even with the old codes.
A buddy's shop uses Spies-Hecker, and they provided a bunch of color samples of reds, greens, blues, etc.
If you can find a shop spraying that brand, look through those and match to an area of your car that hasn't been damaged from exposure.
A color from another car can be tintable if not an exact match.