You can do an advanced library search and limit to "Score" in the Material Type box. By entering a keyword (band, symphony, piano) you will get a large number of results. Adding specific keywords will narrow your results significantly.
If you have a specific composer in mind, do an author search.
Another option is to search by subject in the Field drop down such as Music -- Manuscripts -- Facsimiles OR Music by women composers -- 20th century.
All of our sheet music is in the Fine Arts Library in the Music Building and the staff there can help you locate anything you find in the catalog.