i don't know any way to get it would live.. i know u can buy it from the xbox website but i don't know how that works, as i have never used it... so id start by looking there...
You can go to the website and purchase it, and the DLC will be queued for download on your xbox (put in list for pending downloads). You will need xbox live to download it though, so you won't get any further without xbox live.
I haven't heard of any way other than xbox live marketplace that can get you dead money. My only suggestion to someone who doesn't have an internet connection is that you bring your xbox (or hard drive at least, but I reccommend bringing the entire xbox to avoid any problems) to someone who has internet (preferably a good connection, lol). There you can register for a free silver account (I think you need that to log on, but I'm not 100% sure if you actually need it.) and go to the marketplace.
It's an unpractical solution, but it works.