But eventually I found these plastic models on a stall selling second hand figures:
They have pretty much the look I was after - adventurers in a variety of costumes, not ridiculously heavily armed. They're ready painted, not incredibly well but good enough for a demo game, with a 1950s SF look that should work for the Weinbaum universe. They're actually collectible miniatures from some sort of Star Wars game - don't know what it's called - made by a company called LFL. Most of these are apparently common and were priced at 50p second hand, with a couple at a pound. They look to be about 28mm scale, and (apart from the lack of female figures) are more or less what I want.
I also got a couple of humanoid aliens, which need some head modifications to look human which I'm still working on. One is a woman in a purple catsuit which will do quite nicely as a spacesuit sans helmet, carrying a silly gun, the other is a male figure wearing a heavier suit with jointed armour, carrying an even sillier gun. The woman was originally dark skinned but I want to match a particular Weinbaum character who is blonde, so that is changing.
Anyway, I'm having a lot of trouble finding out about this range - LFL seem to make a lot of different collectible figures, none of which look quite like this lot. Anyone know anything about them?