I think many, if not most, of these keytags were a sort of "group purchase" by a lodge and may have served as a bit of a fund-raiser for the lodge. The blanks were, as PBK indicates, available from several manufacturers. I suspect that the lodge went together and ordered a hundred or so blanks, and maybe a set of letter stamps if they didn't have a set available. Then when they came in, they had a member (perhaps the town jeweler) stamp them for each member, and the member would pay so much for each one.
They make for an interesting collectable - there are dozens of types of blanks, some very fancy and some plain. I find the dated ones the most interesting. Some are found worn almost smooth and others never got much use. The vast majority of them have men's names on them, but I have a couple that belonged to women.
John in ID