Composer scholarly editions are arranged alphabetically by composer in the M3 section upstairs in the Music Library.
Oxford Music Online and the Index to Printed Music can help you locate your pieces within scholarly editions.
Find scores for individual pieces of music published in standard scholarly editions, series and sets from ancient Greece to the present.
Medieval Manuscripts for Mass and Office by 
Search for records for music manuscripts, printed music, libretti, and treatises held in music libraries, archives, churches, and other institutions around the world. This is an open access database.
To find recordings in the library catalog,
An online thematic catalogue of all compositions attributed to Girolamo Frescobaldi (Ferrara, 1583 – Rome, 1643), and a database of the early sources, modern and facsimile editions, and literature.
