hey guys where can I farm this from?

Farm? If you mean the Ranger skill then it's not longer an item that is consumed. It became an active skill that you put in your sub palette in like EP 4?? 5??? So now you use it and it cools down for like 8 seconds and you can use it again. This goes for all grenade skills

If you mean the Braver PA, then.. I'm actually not sure. Let me take a look and I'll reply again!

Sorry, I have no answer. But it's a fairly common drop. Just make sure you're running as many things as you can and looking at all of your PA drops.

Gravity Bomb for Ranger is in the Ranger Class Tree as a talent choice not a PA