Soul Vessel #1 - Majula
Crestfallen Saulden can be found by the monument in Majula. After enough NPCs have arrived in town, he'll give you a Soul Vessel.
Soul Vessel #2 - Majula
This requires a few steps. To start, travel to the Cardinal Tower bonfire in Forest of Fallen Giants. Climb down the ladder, take out the enemies by the bridge, then turn left. This path takes you outside. Go up the gnarled tree, leap to the rooftop, and face the opposite corner from where you entered. See that cave entrance? Now leap from the rooftop to the scaffolding ahead, and head into the cave.
Inside, stop under the first horizontal beam to let a boulder roll by. Now head up the slope where the boulder came from to meet Cale. Speak to him a few times, and he'll give you the House Key.
With the House Key in your possession, you can open the big house near the well in Majula. Head inside, then make your way to the basement, where you'll find a chest containing the vessel.
Soul Vessel #3 - The Lost Bastille
Found in a Pharros' treasure room. See our Dark Souls 2 Pharros' Contraptions guide for more information.
Soul Vessel #4 - Drangleic Castle
Once you take the lift near the Central Castle Drangleic bonfire, you'll find yourself in a room with a cage and three chests, one of which contains this.
Soul Vessel #5 - Undead Crypt
This is found before entering the area with all the breakable rocks, near the Undead Ditch bonfire. If you look down near the movable bridge, you'll see a platform below. Drop down there to find a chest containing the vessel.
Soul Vessel #6 - Memory of Orro
You'll find the final Soul Vessel inside the Memory of Orro, accessed by using the Ashen Mist heart on the fallen giant near the Pursuer boss area. Inside, take the right-side path up the stairs and outside, then make a right. The corpse tucked away over here holds the vessel.