You weren't kidding, this is some old window. What's difficult about identifying your lock is that the sweep part of it seems to rivet directly to the window frame itself. I can tell you with confidence that very few locks work like that these days. I don't think you'll be able to find this anywhere.
Most locks we consider "old" rivet onto a base first, which then screws to the window frame. I say "old" because these are still more modern than what you have here. See our 90-021 for example. You may be able to get something like this to work on your window but there are two issues you have to consider.
If you're handy, then I think you could get a lock like this to work on your window frame. If you aren't sure, though, then my recommendation would be to get a local professional to come out and do it for you.
