What I do is get the color charts then closely match in acrylic, most often mixing a tweak into it myself. But you can get a dealer to mix PPG or Ditzler paint as well. A lot of those old cars use Dupont Duco paint, no longer made. If you can get a good sized screen shot of the chips MCW can probably mix the color for you in either lacquer or enamel. As mentioned I mostly use acrylics now.
Napa store can mix the same way, a sample bottle you need to thin yourself with the cost being around $12 for an oz or two of paint. MCW is pre mixed for lacquer, mix the enamel yourself for about the same cost as Napa but shipping tips the scale big time.
I've spent 8 years perfecting acrylic airbrushing. The old car colors aren't too difficult as they for the most part are not metallic. And buffed up Createx 4050 clear looks an awful lot like nicely buffed lacquer. Still sometimes you hit on some enamels you can mix up easy or see a spray can of Rustoleum 2X you can decant, use a bit more thinner in it and airbrush that.
Here is one example of color chart for 1929 Pierce Arrow, you will need to click the link to get the entire picture: https://paintref.com/cgi-bin/colorcodedisplay.cgi?make=Pierce-Arrow&rows=50
If you search around at that page you can find more years, more car manufacturers etc. I got there though by simply typing into my browser Color Charts Pierce Arrow. I've done it 100 times if once for 1940's cars, model A's 34 Fords and so on, so knew the page to look for next.