I need the code for my cdr 2500 vectra radio serial number gm020543479479 can anybody help cheers john

Your radio is made by VDO and unfortunately the majority of SIEMENS/VDO codes (including yours) will NOT be available for free (or cheap) from anywhere on the Internet as access is required to the original factory database…which is not commercially available..
Try your Main Dealer or a Decoding Service or your local Car Radio / Audio Shop (who are normally the cheapest option) who will connect it to a laptop to read/recode the memory chip (EEPROM)