How do I get black thieves guild armor?
Not nightingale, the black edition,.
It's been so long since I did TG I can;t remember if you get black edition?

Become Guild Master.

Really?!
That takes ages....

All good things come to those who wait.

When you're doing the side jobs for each city just keep quitting until you get a job in the same city from both Delvin and Vex and just complete five of them in each city it goes by faster then you think.

And those who work hard for it (god knows how many quests you have to do to become Guild Master).