As far as i know, the 405th as a whole does not sell armor. We are a community dedicated to the creation of Halo and other video game armor. There might be a few that do sell, however.
If your looking to get armor without making any, your probably better off with e-bay. They usually have it, but it will cost you a lot. I would recommend making it yourself, its not as hard as it seems just read the stickies on the site, follow the instructions, and you'll be set.