I didn't know you could buy pieces at Fred Meyer, but I am also in the US and was 12 when the wall came down. I, too, have a piece (with graffiti!). It was a gift and I don't know where it came from, but my impression at that time was that it wasn't really much rarer than pumice from the Mt St Helens eruption (I have a piece of that, too, or a capsule of oil from the Prudhoe Bay disaster, which I also have in my collection from that era).