This will give you all kinds of ideas. Happy Holidays!
hit up thrift stores and sales for broken instruments and hang those with sheet music on the wall.
Are you looking for decorations or more of a DIY aspect?
I have some old record albums of my parents and would probably display on the walls or on easels. Also other albums would look good. Antique stores would be a nice place to look for musical instruments or other such items . If you have a McKays in your area they have some great selections of music.
Get old music books and make a accent wall with the pages of the music sheets. Mix up Elmer's glue and water and paint it on the wall in sections. Wet music sheets with water and scrunch them up to wring out the water and apply on top of the glue, smooth out on the wall and paint more of the glue mixture over the top of music sheets. Overlap for a less defined look. It will be amazing to look at.