We bought them at hardware stores and gun stores. That was 45 years ago. It was a different time.
Doesn't sound that long ago to me. I was in the service back then. I was big into shotgun shooting back then (still am) and I don't remember seeing any black powder shotgun shells being sold. I guess someone could have had some stashed away in some out of the way store or something. Kind of sounded like it was easy to find the way you were describing it. Back then, it was pretty difficult to even get black powder. I had to get an explosives license just to buy what I wanted to use for my muzzle loading guns. Got easier to get a few years later when Thompson Center started selling their line of muzzle loaders and a lot more shooters go into the game. They lifted the requirement of having to have an explosives license and just limited how many pounds you could get at one time.