The following is a short list only:
In addition to the many non-serial bibliographies in book or article form (just for example, Judith Anne Johnson, J. R. R. Tolkien: Six Decades of Criticism (Westport, CT: Greenwood Press, 1986), or Åke Bertenstam, "A Chronological Bibliography of Books about Tolkien," 12th ed. (July 2015)),