In Nob Hill there's a mall that's not marked on your map. If you look for it you can find it, though. It's to the west of the Impressions and On Thin Ice, and it almost looks like a football stadium on your map. Drive your car through the entrance and keep going down until you reach the actual mall entrance, which is when your map will change to a map of the mall as opposed to a map of Stillwater. On the floor you start out on there's Nobody Loves Me, a punk/biker store that sells the piercings you're looking for as well as leather motorcycle jackets and motorcycle helmets, Let's Pretend which sells all sorts of fun costumes (ninja outfit :D), and if you go up a floor from there there's Leather and Laces, a bondage sort of store.
"I dreamt I was a moron."-Squall Leonhart, Final Fantasy 8 Squall is Awesome