Free music is very valuable, yet not enough people, make a real effort to fully credit and thank the people who create and generously make Music and Sound Effects available for independent films.
I have found Souncloud to be an absolutely wonderful source for Music, as well as a whole bunch of sites specifically designed for sharing.
Watch the Credits on Catching Broken Glass by Terrel Holden and myself shot on a Panasonic GH3, for how I did the credits to thank the sources -every one of them.
https://youtu.be/pRYmZRWZ51U