Changing Radio

I have a 2002 GMC Envoy with the standard radio (AM/FM cd) I want to purchase a GM AM/FM 6 Disc Cd on Ebay, How do I get the unlock codes?

Will the dealer give you the codes with out a problem

Here is something I found out

According to GM if you wanted to upgrade your standard am/fm Cd player to a am/fm 6 disc cd player you cannot with GM's RDS Radio's, The Vin number is programed into the radio and when you start the car the computer checks the vin number in the radio, as long as they match it will work. Not sure if this is the case with the GM Nav, radio


But then again this is coming from GM.