Ebay is where you will find it.
There are more honest traders than scammers on ebay.Look for a long time seller with great feedback.70'S pups have grey bottoms. Ill check into some sources I personally have,but to optimize your hunt I would like to know what the other two pups read.Do you have a meter?:
I would settle on a modern replacement in the same within the same ohmage.
Hopefully you know if you do locate a pup it is going to be costly The plastic covers are in the $150=$250 range(for a set):