Is there a second set you can find? Or can you take Brynjolf's set since he stops wearing it, if so where is his?

bump sorry I just need help

I haven't tried it, but when you go to the Nightingale sanctuary (or whatever its called) the stone you activated to get it the first time is still there and can still be interacted with, and might give you the armor again.

Might try pickpocketing Karliah (if you have the perk though I would save before investing in the perk or attempting to pickpocket her.)

I dunno where Brnyjolf put his. Always the console eh?

You can use the duplication glitch involving the
there are videos on youtube that demonstrate how to use this glitch.

Can you pickpocket the armor off of Karliah when she sleeps? And has anyone found where Brynjolf put his Nightingale armor?