Go to:
http://www.mygmlink.com
Get yourself an account, then register a vehicle that came with a TNR from the factory (VIN not needed). After setting up the vehicle, go to that vehicle's home page, and click on "glovebox" on the left side. Then click on the "Owner's and Service Manuals" link.
You should see manuals you can download in PDF format, including the "View Supplement: Navigation System" link.