There is a good resource at Autocolorlibrary.com.
YOu can print out the sheets there, and they have all the codes listed, with the PPG numbers.
Go to a good local paint store, and see if they can cross reference to get a sample. The guys should also be able to match a chip with a spectrum analyzer.
MOst of the diffuculty lies in the fact that the old PPG codes are DBL (laquer) I think. Nowadays they use DBU (Urethane) If you can find a shop, they might be able to cross reference the number.
If you are going to use waterborne, thats unfamiliar territory here.
Good luck, and let me know how it goes!
Dan