You can give your dealer a ring, give him your VIN and serial number. That's all he will need from you to give you your radio code. I know there are some dealers that give the information for free, but in some cases, they ask for a fee.
If you're not ready to do this, I suggest you check out unlockradiocodes.com. My car battery died on me a couple of days ago and my radio was rendered useless as a result. They were kind enough to give me my code and the guides in their website helped me a great deal as I’m not much of a car person. My radio is working again now so I can definitely vouch for their service. It was free too (just had to fill out a survey!)