Anti theft radio codes can only  be retrieved  at the dealership level from a database by VIN # and radio serial# for someone displaying current owner ship of vehicle.If you got a radio from a salvage yard vehicle that you do not have the VIN # of and Maxi Sys or IDS won't retrieve the old vehicle VIN from radio, there is not much you can do as far as I know except go back to salvage yard ,get the VIN # and search for papers in car for past owner contact  information .