Well, I know for a fact that one of the two grocery stores near me (I alternate between these two)
doesn't sell stamps, so if the other one doesn't...I'm back to square one.
I remember stamps being sold in gumball-type machines at places like Woolworth's or other regular stores. They were larger and more boxy (not the round glass), but you put your money in (slots for nickels, dimes or quarters), place a dial on your selection (or put the money in a designated slot?) and pull a lever and a stamp(s) would drop out the bottom. It wasn't digital (this was years and years ago), just a mechanical, gumball type dispenser machine.
But I've not seen these in quite a long time, now that I think about it. But when I was a kid, I'd always notice them in stores I went to with my Mom or grandmother. I guess those were getting broken into as well (for the money
and the stamps, which carry a bit more value and use than a piece of bubblegum).