If you’re a foreigner they’ll be eager to take you there. Just go with the people saying “DVD! DVD!!!” when you get off the escalator at Computer City. They have hidden rooms in the building or nearby that are filled with their wares, and they know they can trust foreigners so they’ll pretty much take you there without hesitation.
It’s crazy because it’s often a room with a bunk bed and old bicycles or something. They’re halfway living spaces tucked in the back corner of some inconspicuous building. You might be flipping through DVD’s in a cardboard box while this persons kid is playing with toys in the same room, a few feet away. This is a great way to welcome someone to China, hahaha.