The Claremont Colleges Library has a large collection of music scores. To find these sources search the library catalog :
THEN limit FORMAT to Musical Score and LOCATION to The Claremont Colleges. This will limit your search to only Claremont owned scores.
Claremont College users can request scores that the library does not own from other libraries through Resource Sharing
Loeb Music Library - Digital Scores and Libretti - Harvard University
IMSLP Petrucci: International Music Score Library Project