I'll keep my eyes open for the old Mamiyas (seem hard to find over here) and Kievs ...

In the meantime, I've laid hands on a 500C/M and while it's big and heavy, it nevertheless remains a definite possible. Unfortunately the example I used had a little mechanical problem so I didn't buy it. Beautiful machine of course, and the test roll looks deadly sharp despite everything being handheld in dim woodland (mirror lockup is a godsend isn't it?)

However I've also realised if I drop my hankering for a WLF then another possibility swings into view - one of the older Fuji 645 rangefinders. I happen to like 4:3 aspect (though square is lovely), plus with an eye-level camera I can use portrait and landscape.

A GS645S is well within budget, the slightly wider lens is a bonus to me, plus they seem to have a good rep for reliability ... and they aren't 60 years old. Mind you I've got 60 in closer sight than I'd like ...