Check your local area for a police supply store. These stores are open to the public and you can buy whatever you want there. I think you could just get a shirt & vest and just stick some thick cardboard underneath it so it looks like the trauma plates of a ballistic vest. The modern "vests" are not much thicker than a T-shirt, but those SWAT para-military guys wear big thick metal/kevlar plates over their chests that give them that bulky look.