Progress through the game until you reach a certain point in Chapter 5 to unlock the Clan Creator mini-game. Then, successfully complete the first 13 missions in Onomichi. Once you have completed 13 out of the 16 missions, talk to the bartender near the Clan Creator mini-game to unlock him as a member of your clan. He will tell you about a man he knows that operates a Black Market. Shortly afterwards, you will get a text message saying the Black Market vendor is ready to meet. The Black Market vendor icons will now appear on your maps. The Kamurocho Black Market is in the Hotel District area, and the Onomichi Black Market is within the Hana-no-kubo area. The Black Market allows you to purchase rare and valuable equipment.