Other than that... maybe you could look on the artist's website?
In addition to playing around trying to come up with my own mash-ups, I use the instrumentals for Bridal Party Grand Entrances, or at events where the song's lyrical content might be considered objectionable, such as some church events or public events.
Sween: What is the best, easiest, cheapest, most efficient, quickest method of mounting 50" LCDs?
sss18734: Duct tape fits 4 out of your 5 criteria...
Defected Accapellas Deluxe series, a 10 volume series, by Defected Records, with approximately 25 songs per volume.