You can get the buff as a DK using:
- A potion, it's the most common way to get it endgame if you can afford it by either crafting or buying potions
- Igneous Weapons, which is the other morph of Molten Armaments, which also means that, if you want the heavy attack bonus, someone else needs to run it.
- Dreugh King Slayer set, which you can find here. The 5p passively provides the buff, however, as a heavy armor set, you also sacrifice a lot of maximum stamina. It also means you're in for a pretty harsh grind if you want of very specific weapon of this set.
- If you use a 2H weapon, you can use any morph of Momentum, which provides Major brutality for 33s
- If you use DW, you can use any morph of Hidden blade, as they both provide Major brutality for 20s.