This guide collects search tips and links to materials. 

Use the CDs & DVDs page to look for musicals in those formats (also includes Video and WWW options).

Use the Web & Background Reading page to locate plot summaries, actor biographies, and other works about musicals.

Musical Scores are easiest to find in Library Search. Search by musical or song title.  If you want a full list, use the term "musicals."
Use the facets on the the left to limit your search to the Resource Type of "Score" or to the Collection of "Score."