Target, Walmart, Amazon, and the Microsoft Store do not have it listed yet.
Please be patient and wait a while before pre-ordering. After all, there is another six months till the release of Halo 4 
what about the legendery edition?
> what about the legendery edition?
343i already confirmed there will be only 2 version. Default and Limited.
From the bulletin :
Right about now you may be wondering, “If all those things come with the Limited Edition, what are they going to put in the Legendary Edition?” Here is the answer to that question: There will be two options available at retail for Halo 4 - the regular version of the game and the aforementioned Limited Edition. We decided to focus our efforts on a single special edition instead of numerous ones so you wouldn’t have to pick and choose between what ancillary items you want. Now your primary choice is whether or not you just want the game, or the game along with all the goodies. And we’re hoping we made that decision an easy one for you…