Where to find musical tracks to record

[Charles Snyder]

I have seen references to buying musical tracks but have no idea where to look. I sing primarily big band and Sinatra music and would like to get some soundtracks to make clean karaoke discs. The devocalizer programs work okay for some songs but there always seems to be that ghost voice in the background which is annoying. I would like to have some pure soundtracks without vocals if they can be had.