While the library catalog is the best place to check for specific items, if you just want to browse the shelves, the following call number ranges may be helpful

RM1500: complete operas

RM1505: arias and other vocal excerpts from operas

RM1527: stage musicals

RM1527.2: movie soundtracks, including musicals

RM1528-RM1529.5: secular duets, trios, etc., for solo voices

RM1619: secular songs by multiple composers (organized by singer)

RM1620: secular songs by individual composers (organized by composer)

RM2018-RM2019.5: sacred duets, trios, etc., for solo voices

RM2102-RM2114.8: sacred songs for solo voice