A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

For advanced projects, follow bibliographic trails
Finding useful sources
Part I. Research and writing: from planning to production

If you're into advanced work, use the bibliographies in your sources to find new sources and use their bibliographies in turn to find more. Do this:

Skim bibliographies of recent books on your topic; look at any work mentioned in all or most of them, along with other publications by its author.

If you find a source useful, skim its index for authors mentioned on four or more pages.

Look for reviews of research in the first few paragraphs of journal articles.

Look for recent PhD dissertations even marginally on your topic. Almost every dissertation reviews research in its first or second chapter.

New sources are best, but you may discover an old one with data long neglected.