The only time I record my own baking track is if I do it acappella Warbler style or play the piano. Otherwise, YouTube is a pretty comprehensive source for baking tracks. Sometimes I'll use an original artist's version instrumental, sometimes I'll have to edit that into a Glee version myself - doing things like changing pitch and cutting. My recent New York State Of Mind cover is an example of some heavy editing I did myself to the baking track with the difference that I actually purchased that backing track from iTunes - which is an even better source for instrumentals but costs money. But the best ones - my last cover is an example of this - is when someone extracts the baking out of the actual Glee version leaving you with the Glee instrumental. There's always a few YouTube channels doing things like that but they get shut down pretty quickly because obviously it matches up with copyright issues. Plus a con for those types of instrumentals - they're used for other things too, not just Glee - is that there is often an reverb echo of the original voice still present.