This is supposedly one of the more frustrating pieces to get your hands on since it appears to be a rare drop from the patriarch. In fact, when I got mine, I bought it in the Bazaar for 1k. The Patriarch generally pops up in one of the shelters or fort in the snowy mountain half of DL, so don't just park yourself in front of one of them and expect him to pop-up eventually. Go check each of them.