You are a Volvophile :)

If the radio is original to the car, the Volvo parts dept can get you the code if you supply them with the VIN. Normally, they will not do this over the phone, you will have to do this in person.

Sometimes, people write the 4 digit number on the radio casing. Pull it out most of the way and see if there are any numbers written on it. They must be between 1 and 6, usually starting with 3?
If the owners manual is in the glove box, scan through it looking for the number. I always write mine in the radio section :) The card with the number on it always gets lost.

Klaus