Unlocking and playing dark wizards?

[The Good Dave]

I finished the game through on story mode. The Bellatrix and Voldemort tokens are filled in when I hover over the last level in the Leaky Cauldron. I'm not sure how to unlock or use or find any other dark wizards, and I don't think I can play until I unlock another million studs to buy Bellatrix in Madame Malkins. Where can I find other dark wizards? I've read I unlock Grindelwald somewhere but I can't find it. It's getting to be a bummer playing through again with no dark wizards. Thanks!

[BushwalkerSP]

If you need a million studs go to Borgin & Burkes and complete the bonus level. You will find Grindewald token in the Tower.