I am trying and failing to find a particular paper. My university's library catalogue, Google Scholar, and Google all came up empty. I even tried the catalogue of the paper's institutional affiliation, but they didn't have it either. It's possible the paper really has been lost forever, but I find this unlikely; it is a significant paper that still gets citations. What other avenues exist for finding this paper?

*Note to readers: this is a frequently-asked question and so we have compiled this "canonical" post to amalgamate some of our best answers on this topic (per [this](https://academia.meta.stackexchange.com/questions/5166) meta discussion). Questions requesting individualized help finding a particular source will be closed as a duplicate of this: we hope these "hints" will be helpful, but  tracking down individual papers is not our role.*