I was not aware there were halo 4 codes until recently and would like to unlock them but after searching for a while i can’t find them do they exist?
You can find all them on our Wix site here (one of these days we’ll get that updated and moved to a better location). Also, if you search for //CLASSIFIED//SECTION 3 in the Halo 4 forums, you can find a list of our release topics which has some more info on unlock requirements and rewards 
To redeem them you need to use the Halo Waypoint app on the Xbox 360, there is no way to do it on the website any more and no facility through the Halo Channel
you have to download halo waypoint first(if you haven’t already), then you press the blue X button on your controller twice. Then the screen will show a bunch of symbols. You will then input the code you wish to enter, and if your code is correct, the backround of the screen will flash sky blue twice, and it will take you to the next screen, where you receive your reward. Its easier than it sounds.
Thank you