1965 Dodge Dart 270 defroster vent color.

Sorry to hear you’re have such problems. You’re not alone; I was helping some model car companies with getting the proper muscle car colors on their products but these companies were based in Europe. I remember Ford “grabber orange” for the ‘70 Trans Am Boss 302 models were a problem & Penske dark blue.
They had the same difficulty and were told “those are really old colors & we don’t have the info”.
I had to get some small samples mixed to use as samples to get copied.