Or not even as a King but just a noble, heck, a very wealthy individual - you should be able to place an order at the local smithy to make you X amount of X types of armor. Ok, from a RP perspective, this would take a long time with big purchases. One does not simply make a plate mail in one day. So thinking about it maybe it would make more sense if you placed an order at the local guild master. He would then contact smiths through the kingdom or maybe just through entire land (merchants aren't bound by petty borders after all) and in few days time caravans from all around will come bearing armor to you. And once you do become a king (or a VERY wealthy individual), you could hire professional weapons/armor smiths for your ironworks (you can already set up by default in M&B:W) and they will produce weapons/armor en mass.
Of COURSE, you could also just have a guy who would magically have his inv full of best herald gear. Less hassle. Because if one would really like to expand on how you acquire weapons and armor, why stop at yourself/companions? Make a system where your entire army has to have physical access to gear in order to upgrade, instead of you just paying some frivolous amount of money and suddenly your troops are pulling high-end gear out of thin air. Dunno, personally I would absolutely love if there was some more complex system behind managing your army. But I doubt I'll see anything like this in any game like M&B soon.