You need the spell Reducto to access this section. This is also the place where you can unlock the character Voldemort (requires all 200 Gold Bricks) and a handful of other characters. You can find the silver gate that you must unlock in front of Eeylops Owl Emporium in Diagon Alley.
Igor Karkaroff – You'll immediately see this token a short walk from the gate. Use WiLe on the wooden planks to build a stair to grab it.
The Bloody Baron – Stand on the cart and shoot it. You'll be launched upward and get the token as well.
Shifty Wizard – Continue along the path and you'll come across a table. On top of it is a chest that has some vines. Destroy it and shoot the table. Wait for it to move near the lamppost then stand on the table as it launches you in the air, grabbing the token along the way.
Enter the shop to the left then grab the gold brick right behind the main desk.