Use a music search engine or radio station such as Pandora to begin discovering new instrumental music or specific pieces you would like to find. By typing in the name of an artist or genre of music, Pandora will generate a playlist of related compositions and songs.
Purchase sheet music arrangements of popular songs or movie scores at audio retailers such as Guitar Center or Sam Ash. Each of these retailers includes a listing of their sheet music collection on their websites.
Search for specific classical compositions using online sheet music retailers such as Pender's Music or Burt and Company. Each of these distributors carries a large selection of popular and less performed classical works.