Worldcat says it's at 1483 libraries: https://search.worldcat.org/title/Structure-and-interpretati... (although some of them may not participate in ILL, and some may only have eBooks that you probably can't borrow unless you have an appropriate account)
I'm sure SFPL does tracking on ILL requests and if something comes up more than once or twice in a reasonable period and it's available for purchase, a copy will be purchased to add to the collection.
And I can't request a copy because it's too old.
Do you believe that no one in San Francisco ever wanted to read SICP?