unlocking a chevy express radio

i purchased a factory radio for my 2006 chevy express rv the radio came out of a 2005 gmc van would any one of you fellows know how to unlock this radio the auto salvage yard i bought it from says its locked when they went to test it after they removed it

it will become "locked" when you disconnect the radio from the battery.

dealer will provide ya the code for 20-30 bucks