These sources are good for finding background and general information on a composer, composition, or musician. Use and cite general information from these sources rather than Wikipedia. NOTE: Some instructors do not count encyclopedic sources towards your source requirement.
These databases are your best bet for finding scholarly resources about music and composers as well as viewing musical scores in the public domain.
(Johns Hopkins University Press) Full-text articles from "over 300 high quality humanities, arts, and social sciences journals."