Resources are extensive--but--not in a single location because of format or condition.
Browse stacks for scores, recordings, videos, librettos
M1500 full scores; complete recorded performances and videos usually include libretto and translation
M1503 complete piano-vocal scores, and recorded selections, both usually include lyrics with translation
M1507-08 piano-vocal anthologies of arias or show selections
Table 7A anthologies by vocal range from musicals and Nico Castel opera librettos with IPA
ML48-ML50 separately published librettos and lyrics; older librettos housed in Rm 209, Bay 40
"Vintage" stage and film single song sheets housed in Rm 209, Bay 68
Dance orchestra scores and parts, housed in Rm 209 top perimeter, 10-29
Search via BU Library search consider narrowing results by Material type, Language, etc.
for writings about people, topics, genres consider using Advanced Search by Subject keywords
Sondheim; Opera Russia; Musicals
for certain title searches, consider using Advanced Search, Title Starts With,
1776; Ring; Pippin; Nixon in China
when in basic search, type enough relevant keywords, use of quotes for phrases can help
Tobias Picker opera Claiborne; Puccini Un bel di; "bushel and a peck"
Finally: Boston University's Howard Gotlieb Archival Research Center houses significant and unique collections, many connected to music and the performing arts. After discovering HGARC items you wish to consult--search their site in addition to BULS--next be sure to contact them at email@example.com to arrange your visit.
A 1971 recording ot The Red Detachment of Women is in the Music Library's Listening Room.