As the reader, you can also ask [mathoverflow][1] for help finding the paper.  There have been some very interesting MO questions along this line.  In particular, this record helps others to also track down the same paper (or discover it never existed in the first place).  Feel free to add to this list since this is CW:

 - http://mathoverflow.net/questions/199678/scott-solovay-unpublished-paper-on-boolean-valued-models-of-set-theory (never existed)
 - http://mathoverflow.net/questions/122888/looking-for-a-copy-of-leo-harringtons-unpublished-notes-on-the-first-nonproject (now we have a version online)
 - http://mathoverflow.net/questions/175737/harringtons-unpublished-note-the-constructible-reals-can-be-anything (now we have a version online)


  [1]: http://mathoverflow.net