I occasionally find a dusty bottle at a liquor store. It's funny though, once folks try it, they nearly always love it. My friends still chuckle about a time that I brought a bottle to a cookout and everyone was like "ha ha, you anglophile! pip pip! cheerio!" but about two hours later everyone was walking around with Pimms Cups as they tried it and made one for themselves.
What I really want to try is Pimm's Winter Cup, the brandy version, but it's firmly only available in the UK.