Also, you can contact the Harry Fox agency. They are the representatives for many of the publishers. If you are definitely doing backing tracks with signature licks, it might be easier just to pay the royalties than to hire a lawyer. http://www.harryfox.com

At one time I was interested in selling MIDI file backing tracks, and this was the starting point for me.

Notes
Brand new 2012.5 updates from Norton Music:
  • 2 new style disks for Band-in-a-Box
  • 2 new free (with a purchase) fancy intro/ending disks for Real Band and other DAW's
  • The Ultimate Gospel Fake Disk
  • The Real Rock Fake Disk (plenty of classic rock in this one)
  • The Beatles Fake Disk
  • And an updated Christmas Fake Disk

Hundreds of Free .sgu and .mp3 demos for the above at: http://www.nortonmusic.com