I have bittersteel and I'm only rank 9 - I think I got it about rank 5.
It's totally random, just keep playing the game normally, or go DO on all three characters it will pop soon.
English
-
I'm DO on all my characters, 29 on my main, 4 on my alt, and 7 on my warlock.. Nothing but armor pieces and guns :/
-
Well I can't suggest anything else then. It's random it could pop next level it could take another 20 levels.
-
Hopefully it comes sooner rather than later :)