Yinzers is my absolute favorite shop around, and is THE place in the Strip District to get your Pittsburgh gear.
Located at the far end of the Strip, I would highly recommend holding off on buying any clothing or knick knacks until you make it here first. If for some reason Yinzers doesn't have what you want, then you can give yourself permission to venture out and purchase things elsewhere. This store is a two-story mecca of all things black and yellow. The place is bursting with any item your heart desires, so long as you're desiring it to be covered with gold and include a Pirate or Penguin. They have such a large inventory that many of the sale clothing items spill out onto the street and around the corner. You can buy everything from a Heinz Ward ornament to a dubious golf-bag wielding Alex Ovechkin t-shirt. (It's still one of my favorite t-shirts to this day, but if it's worn anywhere outside of Pittsburgh, it's an awkward conversation starter to say the least.)
I've spent one too many dollars at Yinzers, but it's all worth it. The next time you're in the Steel City, bypass the sketchy seconhand dealers and came straight to the og, Yinz!