I recently found a whole pile of "ballroom" style CDs in the charity shop around the corner. I got a 4cd box set, (Victor Sylvester I think), a 2cd set, "Sapphire in Sequence" and several individual discs. Got the lot for a tenner and so far haven`t found a duff track.
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For standard Waltz, Fox-trot, Quickstep etc you can most likely find dozens of tracks which are already in your collection. For instance, Fairgound Attraction`s "Perfect" is a Quickstep... listen out for others of the same tempo.
You can apply this to a lot of stuff... listen to a Foxtrot, or a Tango, or whatever, and try and match it`s tempo with songs you already have. But...
Don`t try this if you are asked for Strict Tempo Sequence dancing. Make sure you have the right track for the Valetta, Paul Jones, Eightsome Reel and the like, as the number of bars per sequence is crucial. Play the wrong track and make sure your camcorder`s running for when they all fall over