Downloading a music mp3 for mixing

Help a beginner, please? Mac Desktop OS X 10.5.8. I am desperate to find a website that offers either a free or a paid-for mp3 download (in fact, of Bach - Prelude 1, BVW 846, but that is irrelevant) that I can use to mix in as background to voice. I can find plenty of mp3 downloads but all they will do is to play the music and leave no link.

You can use the SoundFlower software to make your Mac record anything playing on the computer.


Thank you! Soundflower (nice bane) installed. Most grateful.