This is probably the best way to buy armor here: go to walmart, get some paper and glue, and get to it! its not that hard to make a decent set, most of us are working towards a full suit at some point. From what i can tell most people who DO sell items on here do limited runs of castings from their own pieces. that means that A) they have to be the same size as you, and :coolthey have to want to sell you the fruits of their labor. Weapons are probably more easily obtained, because no one likes pepping them (I absolutely hate making them myself, going with the toy plasma blasters for my first one.) But you have to get vetted to even see the classifieds, and from what i can tell they actually check your posts to make sure you are meeting certain criteria, not just posting hi 100 times. so go to tamasoftware, get pep designer version 3.something, and join the club hehe!
Edit: or you can look for the rubies halloween costume on ebay, saw one months ago, like 900 bucks plus shipping, and then you can be Plastic Chief!