If the code is not in the manual, you can take it to a deal and they can look it up for you... the code in my manual was WRONG and so i took it to the dealer... they did it at no charge.
one thing to note - for the dealer to get the code the radio needs to be at the point to enter a code - if its locked, the car will need to be on for an hour to reset...
i also read a thread that said their code was on the back of the radio - i don't think that is true for all as isn't one of the reason for needing a code so the radio won't work if its stolen?
anywho - good luck!