In Australia you have to go to a VW dealer who can get it off their computer. Normally its written inside the owners handbook kept in the glovebox. If you're worried about having no radio if/when you change the car battery you can buy a "memory saver" device which goes in the cigarette lighter socket and keeps a supply of power to things like the radio whilst the batttery is disconnected. If so inclined you could also bodgy up something to do the same thing.
Does the radio just unlock or does it also give you the code? Most recent models now will unlock themselves after loss of power as long as the radio is in its original vehicle. More or less knows it's "home".