If you wish to search for music scores/sheet music in the library catalogue, simply type the title of the piece of music you are looking for into the search box and click search. Then refine your search using the format refinement of 'score' on the left side of the page.
e.g. "Bran Nue Dae"
If you want to search generally for music where you do not know the title or if you would like to browse, type in 'music' into the search box and again refine to 'score' giving you over 63000 choices.
The following sites provide free downloads, but take care as some items may still be in copyright.
Purchasing Sheet Music: Most of the following are commercial sites: