They crop up in discussions here regularly ... just search this forum (EUBs not the whole of talkbass) for Harmon.
Regarding finding one in the UK I wouldn't hold your breath
I've seen two discussed on basschat.co.uk (and it's predecessors) in the last couple of years. I's difficult to track them down on, for example, eBay, because of the huge variety of brandnames they're sold under ... check the other threads on this forum.
Andy