It used to be easy, a few years ago, to get passwords to the Sanborn maps online. Even for the whole USA. But that was slowly choked out, for whatever reason. I guess they want you to pay for the access. Anyhow, you have it figured out that .... yes .... a library card gets you access, if your particular library is signed up. I have it through the San Jose Library, for instance (they have only the CA sanborns for their access).
You've got to simply contact each library in your area, and find out if they have them. And actually, since most public libraries are on-line (ie.: have websites), all you need to do is simply go to their website, and look around. You know, like click on "on-line resources" (or whatever), an so forth. Keep following through the chain to see what they offer. Or perhaps they have a key-word search, and you can try "maps" or "sanborn" etc... Try not only city libraries, but also university libraries.
Once you find out which library has them, then it's simply a matter of getting a library card. This can be tricky since they might require you to be a resident of that particular city or county? Or a student (or staff) at that particular college? I dunno.
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