Nope. I'm most disappointed - it would've been really easy to use them, if they had been.

Now there are such things - MailBox Etc. does a 24-7 access service throughout the country (and indeed the world), but they only started in the US in 1980 and I need this to have been going at least since late 1978.

I do vaguely, vaguely remember something about little boxes with keys. But all I can think is some local shops had some kind of service which was similar.