Welcome Patrick,
99.9999% of the members here buy their armor, that other .0001% consists of the armor makers that are members here. So maybe you were meaning you wanted to buy an assembled set of armor? As Jenny mentioned I'd stay away from assembled kits as it's much harder to re-assemble and trim it to fit you when it's already been fit to someone else. With the tutorials here and all the build threads you'll be able to put your suit together. All it takes is thorough reading and some patience.
I don't see where you're located, but your local garrison will be instrumental as well.