In addition to the resources recommended in the Music Resources and Media Resources pages, try searching in these interdisciplinary resources.
JSTOR is great, but don't stop there, because you may be missing out on newer content that is not yet available in JSTOR. Be sure to search in multiple databases, both general (this page) and discipline-specific (music and media pages).
If you find a thesis or dissertation of interest in ProQuest, be sure to search for publications by the same author in the Library Catalog and the Articles & Full Text search. That author may have published articles or a book on the same topic or related topics.