You'll often find a wealth of other sources by looking at the bibliographies of the books or articles you've already found. This page will help you know how to chase those sources down.
This is a citation for a chapter in a book. Notice that there are no volume or issue numbers in this citation, and there's a place of publication and publisher listed:
Weiner, Serh. "Spenser's Study of English Syllables and Its Completion by Thomas Campion." Spenser Studies: A Renaissance Poetry Annual III. Ed. Patrick Cullen and Thomas P. Roche, Jr. Pittsburgh: University of Pittsburgh Press, 1982. 3-56.
This is a citation for an article in a periodical. Notice the volume and month/year in this citation:
Willcock, Gladys. "Passing Pitefull Hexameters." Modern Language Review 29 (1934): 1-19.