IMSLP/Petrucci Music Library: Download and print full scores and complete parts for public domain music.  Their iPhone/iPad app provides an easy access to the library.

Orchestra Musician's CD-ROM Library: Provides complete orchestral parts for the major works.  The music library currently holds volume 1 through 12.  The CD-ROMs are on reserve and kept at the music library service desk.

Orchestra excerpts books are available in the music library for check-out.  Click HERE to find out the selected orchestra excerpts books that the music library has.  They are located in the MT (call number) section.

Tsukasa may be able to help you find excerpts that you can't find in the above sources.