Note: You won't come up with much if you search for "vocal pedagogy" in the library catalog. Try this instead: "singing--instruction and study."
More helpful subject headings for searching the catalog:
Bel Canto.Larynx.Singing.Singing--Breath control.
Singing--DictionSinging--History.Singing--Instruction and Study.Singing--Interpretation (Phrasing, dynamics, etc.).Singing--Methods.Singing--Periodicals.Singing--Physiological aspects.Vocal cords.
Voice.