Your typical punch-gaurd isn't going to look much like the gear that the shotos wear in Street Fighter. Also, if its worth asking, which game are you talking about? In each of the games they tend to have different designs (SFIII actually has the easiest to-make, in my recollection).
As an aside, keep in-mind that Ryu/Ken/Goki don't actually study shotokan karate. Its ansatsuken (assassin's fist).
PAX East 2012/Anime Boston 2012