You should be wary if anybody is offering you an Xbox live code in return for your user name and password or any other personal information. Even if they promise to help you, it is more than likely that they will simply hack your account. There are websites, chat rooms and a variety of forums across the internet which discuss and offer ‘Free Xbox Live Codes’ but be aware while you are using these websites because many of them just lead you to advertising for affiliate links and you will not actually find what you are looking for.
Cheats or promotional codes can sometimes be found in gaming magazines or on the fan pages of a particular game. The Facebook fan page is usually a good place to start as well as the website as promotional codes may be released here. Promotional codes usually expire at a certain date or when they have been used a certain amount of time so it is unlikely that any code you are given on the internet will work.