Hopefully I can help..
Unfortunately with the majority of those units SIEMENS/VDO/Delco security codes aren't easily available for free/cheap in any case from anywhere on the Internet . as access is mostly required through to the original factory database,vauxhall...The usual advice really with anyone with those units or any other Vauxhall unit that come to justanswer is to try via your Main Dealer and they maybe able to help & access with cross reference with the vin provided its the same unit from new via their database the code for that particular unit or supply another car pass card which all those cars came with that have your codes on it,you would certainly need to check for that through all the cards documents etc/glovebox just in case ....You can also try a local Radio Decoding Service if there are company's local to you that can do that or better still a local Car auto electrics Radio / Audio Shop who are normally the cheapest option if you don't want to go near the Dealer. provided they have the equipment of course, who will connect it to a laptop etc to read memory chip (EEPROM).. either way those are unfortunately the best ways as above to get the correct code you require for you to get your radio working up and running and avoid getting the wrong code and locking onto safe mode..As you maybe already aware there are a few radio decoding websites that do generate codes using the serial number if you can remove the radio unit.but you'll need to be prepared for a fee which can be in excess of upto £20-£25 average..Personally i would try a good local audio specialist "provided they have the equipment" first.. if they can't help. then ask them if they can recommend anyone else locally who can. as there is bound to be somebody out there other than the dealer that can do this i would assume at a much cheaper cost if possible..I do hope this helps