I just ran through all the usual, and a few obscure, paint sources. Take a side cover to your nearest auto paint supply, tell them to scan it and set you up with a rattle can or 3, depends on if you want a full respray or just a touch up.

You can get factory match paints for Indian back to 1901 (Dupont), HD back to about 1909, most of the sites only list back to about 1992 for Suzuki, and mostly for sport bikes.

If there is a Sherwin Williams nearby, they can in fact scan and match auto paints... so can a full line NAPA or Carquest...

Maybe talk to Shovelbum87, she knows about paint.