Not kidding, it really is difficult to find it in the UK. Just phoned up ten offy's in the yellow pages, got four answering machines, and the other six all said they don't stock it. Oh well. I've kept a log of it, so I know which four had answering machines - I can try them again some other time. There's loads more numbers I haven't even tried yet. But failing that, it looks like I'm going to have to find a specialist.