I’ve used this free site to locate and download full midi interpretations of many songs:
http://www.midiworld.com/files/
I then import the .mid files into Anvil Studio, isolate the drum track, change it specifically to a rhythm type track (found out through trial & error that it works best with the BBM), edit into loops and then import the loops into the BBM to construct songs. It makes it a bit easier than creating alot of the beats from scratch.