Public Domain Music
There is a very good site called public domain review which explains everything you need to know about finding music which is in the public domain.
“Works in the public domain are those whose intellectual property rights have expired, have been forfeited, or are inapplicable. Examples include the works of Shakespeare and Beethoven, The King James Bible, most of the early silent films, the formulae of Newtonian physics, and the patents on powered flight. The term is not normally applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as “under license” or “with permission”.” (Wikipedia)
Some examples for inspiration are Handel’s Hallelujah Chorus
Scott Joplin’s Maple Leaf Rag
Or some Country music from the Carter Family
Find more on Internet Archive
