Wayne,
You could get the "real" paint colors mixed at an automotive paintshop, or parts stores that provide paint products. Most of the paint manufacturers will mix the old colors in the old type paints, such as emamels, not ACRYLIC) or old lacquers. However, they usually want a minimum order of a gallon.
What you can do is get the color "MIX" ratio and mix your own. Testors has a selection of the 50s era pastels in their Model Master paint series. They also have some variations of pastel colors in their small bottle series. You could use these and either lighten or darken them to get close to the color you want.
If you decide to mix your own keep in mind that the colors called for in the mix are "True" colors or "standard" colors, e.g. titanium white, cadmium yellow, etc.
I remember reading some time ago about a small operation that was making paint for model cars to match OEM colors. If I recall correctly the company was either in Illinois or Indiana. Anyone out there know anything about this. I know Testors just released a series of car colors, but from what I have seen so far the colors are for mid to late 60s, and early 70s, Muscle Cars.
As a side note the black/yellow paint scheme was very popular in 1956. There is a real
(1:1 scale) black/yellow 56 Crown Vic less than a mile from me. I stopped to get pictures a few years ago, but the owner refused my request and was nasty about it. You never can tell. Maybe it was something I said? Let us know how your Sunliner comes out.