where can i get the black hole weapon mod?

[Parzimav]

saw someone using it and its my first time seeing one

[Caldwell UpperCunt]

It's a boss weapon Aphelion from the foggy world where you puke. Check out the guides online to see how to obtain it.

[Schalimah]

You are probably refering to Starkiller which is a reward for beating the game on apocalypse difficulty.

[Lv 3 Moss Finder]

Beat Apoc difficulty and you can buy the gun with it from Brabus. But also Brabus' post game shop additions a bit bugged right now and they don't always show up for people after beating the game.

[Parzimav]

thanks for the insights guys!