There are a couple of options but going to the dealer is usually the easiest unless you live a long distance away. You can get your code from Becker (
Becker Autosound Website) via fax or mail but you have to submit proof of ownership, a Becker form and a fee. You'll also have to pull the radio (easy - but you need "radio keys") and get the S/N off of the back. The dealer can use the VIN unless the radio has been replaced.
Beware that inputting the wrong code especially more than once will cause the radio to display 'WAIT' rather than 'CODE' and the key will have to be left on for an ever longer time.
The code is a 5 digit number. If you have any service records from a dealer look in the little box with misc info for a 5 digit number with no description.