Local ppg seller told me the same thing years ago. Only a few 1970 colors are available in base clear, but several more were available in single stage and the Delstar enamel system. Maybe buy a small batch of the paint in another line and then pay them to mix up some base that matches the color? It may take several test spray out cards and trips to the paint store to get there though.

If you have an original part that has B7 on it they can work from that as well.

SPI makes a polyurethane clear that can be applied over other base coats. People who have used it claim it lays down smoother and sands and buffs out easier than the fast drying bodyshop production clears.