The best way to find music in the Cambridge libraries is to start with iDiscover. Type some keywords into the search box and press Enter or click on the spyglass to get a list of items (scores, CDs, LPs, DVDs and more) from libraries all over Cambridge:
You can then refine the results to the type of material you want using the Resource Type option on the right-hand side of the results screen.
In the University Library Music Department, you might need to search for items in old-fashioned card drawers, as roughly two-thirds of its notated music isn't currently searchable online. The University Library Music Department also has a backlog of items that haven't been catalogued yet. If you need one of those, don't give up: library staff are there to help you (check the opening and staffed times for the Anderson Room here).
It may also be worth checking to see if your college library has any music collections. Many have CDs and some also have scores, including full orchestral and choral sets.