Exit the Basilica complex, and return to the church’s façade. Take a left on the alley next to the side wall of the church, and walk to the back of the Basilica, along Largo Piero Bargellini. Continuing straight onto via San Giuseppe, you’ll find the entrance on the right side, at number 5r. Go in, and cross the courtyard following the signs, until you find the stairs to the shop.