You cannot find this stuff on the official Xbox website. Here is the legal grey area workflow used by preservationists.
XBOX_360_DLC_2 (Internet Archive)
The Xbox 360, released in 2005, was a powerhouse of gaming innovation, bringing high-definition gaming to the masses. One of its most beloved features was the ability to download additional content, known as downloadable content (DLC), which expanded games with new levels, characters, and game modes. In this feature, we'll dive into the Xbox 360 DLC archive, highlighting some of the most notable and iconic DLC packs available for the console. xbox 360 dlc archive part 2