Use the R.W. Steen Library Catalog to look up print and electronic books, as well as other locally-held materials. Click on 'Musical Score' under the 'Format' heading to limit your search to printed music.
Search RISM's online catalog of over a million primary sources in music, including manuscripts, printed music editions, libretti, and treatises housed in libraries, archives, monasteries, schools and private collections worldwide.
The composer's 'Works' list in Grove Music Online may also provide help locating rare and difficult-to-find scores and manuscripts.
A gateway into music research, including the latest full-text of New Grove Dictionary of Music and Musicians, New Grove Dictionary of Opera, and New Grove Dictionary of Jazz. Subscription limit: 11 simultaneous users.