This inlet actually came in a big box of U.S. fittings which I acquired from a local junk shop a few years ago. The owner had no idea what these "weird" plugs and sockets were for and thought that nobody here could ever want them, so I got the whole box for about £1!
I've had the box stashed away in a cupboard until deciding it was time for a tidy up a few days ago. My best bet is they found their way here from one of the North Sea oil rigs, as I know some of the oil platforms are wired to U.S. specs.
As well as many NEMA twist locks (30A 600V 3-ph, 20 and 30A 120/208V 3-ph, etc.) the box included about four dozen non-NEMA panel mount twist-lock receptacles, dual rated for 15A @ 125V or 10A @ 250V.
Of more immediate value to me, there were 30 round, panel-mount NEMA 5-15 receptacles still in their boxes with screws (also Hubbell). They'll be just the job when I get around to making up some distribution panels for my 120V gear. Well worth £1 just for those.
[This message has been edited by pauluk (edited 06-12-2006).]