This is only a sampling of online collections containing historic sound recordings, documents, and scores. If you are interested in finding other online resources, take a look at this more comprehensive guide from Harvard College Library:
Although Bertrand Library does collect CDs, DVDs, and a limited number of musical scores, most scores and sound recordings are kept in the Music Library located in the Sigfried Weis Music Building, Room 120. For more information about the Music Library, click here.
You can find scores and recordings available in both Bertrand and the Music Library by searching the WorldCat Library Catalog. In the Advanced Search, limit the item format to “music” or “musical score.” Or, after typing a search term into the catalog, limit your results by format using the menu on the left side of the screen (you can select “musical score,” “music,” “CD,” “LP,” etc.).