Just following up this thread in case anyone's interested, I got a Hohner Marine Band the other day, and comparing its physical appearance with the Echo Super Vamper, it looks almost identical, apart from the name stamped onto the chrome-plated top, of course. I haven't looked inside to see if the reeds look different.

The sound is near enough the same as far as I can tell, although I can't make an exact comparison, because the new one I got is in a different key from the old ones I still have.

Anyway, the Marine Band looks pretty much a replacement for the ESV so I guess my question's been answered. Thanks to all who chipped in with their five pence (or cents!) worth.