Someone here had the suggestion that I pose the question to Hillbank, who forwarded my question to the factory.
Good news - Hillbank responded to me, but with something considerably more elaborate than a simple paint code.
Less than good news - I have not been able to find a local vendor who can decipher the mixture details for me. Not yet, anyway. Or anywhere here in the U.S.
Maybe someone here will have more luck, so I have posted below what I received from Hillbank.
For reference, I found a supplier on E-Bay that has the basecoat. In Germany
I might have found a potential vendor, Micro Auto Paint in Highland Park, Michigan. They seem to carry and / or mix Glasurit. I will give them a call tomorrow and report back here what I learn.