I don't think you will find them in grocery stores, I googled and came up with nothing. I'm pretty sure WAY back when, my parents did buy them in a store. Now I order online (hard to pick them up anyway given the distance

).
DD2 found a can at a store in Kyoto, Japan when she did her semester abroad. Talk about totally unexpected! Kind of like 35ish years ago when we found Ben & Jerry's ice cream in the British Virgin Islands at a time when they were still pretty small. They started in 1978 in what had been a gas station in Burlington. Free movies on the wall of a building next to their parking lot on Wednesday nights..
These olives are not like any other olive I've had. Certainly not the flavor of a green or Kalamata olive (I don't care for either). Closer to black than anything else, but not. A bit of a nutty flavor. They are shades of medium to dark green to mottled brown. They are not pitted. My aunt (1920-2013) loved them so much that she would hide the pits under a lettuce leaf on her plate so her parents wouldn't know how many she had eaten.
They are not cheap, mostly we eat black pearls on our salads, the Grabers are for special occasions. Except for DD2, she and her sister have split a 12 can case for a number of years at Christmas (no NOT in the toe of their stocking!

). DD2 eats one can for lunch every other month.