Can be traded for the Flexile Sentry Soul with Straid of Olaphis at the Straid's Cell bonfire in The Lost Bastille.
Start from the Soldier's Rest bonfire in Forest of Fallen Giants. You want to enter the house directly across the gap in the ground here. There's a corpse inside that holds the sword.
Black Dragon Greatsword
Received upon reaching Rank 3 of the Dragon Remnants covenant. See our Dark Souls 2 covenants guide for more information.
Black Knight Greatsword
You'll find this after moving through Belfry Sol back into Iron Keep. Before dropping from this caged area, interact with the right-side wall to reveal a hidden chamber. Inside are two chests, one of which holds this blade.
Black Knight Ultra Greatsword
defeating The Duke's Dear Freja, you'll head down a hallway and face a
regular enemy who drops the Brightstone key upon defeat. Once you've
acquired this, head back to the chapel by the spider web pit that took
you to the boos room. Open the door here, then the next to find a chest
containing this blade.
Black Scorpion Stinger
you first enter Doors of Pharros, look in the corner of the watery
chamber for a chest. Well, it looks like a chest, but it's a Mimic. Kill
it to have it drop this weapon.
You'll encounter Bernhart of Jugo multiple times during the game: by the Shaded Woods entrance, by the Pursuer boss area in Forest of Fallen Giants, and inside the Memory of Orro. He can also be summoned into battle with you if you've spoken to him and are in human form. Summon him three times into battle, then speak to him to receive his sword, the Bluemoon Greatsword. Alternatively, you can just kill him, and he'll drop it; however, this negates the trophy/achievement for inheriting his equipment.
Can be traded for the Old Witch's Soul with Straid of Olaphis at the Straid's Cell bonfire in The Lost Bastille.
Can be traded for the Old One's Soul with Ornifex near the Lower Brighstone Cove bonfire in Brighstone Cove Tseldora.
First, you'll need to join the Brotherhood of Blood covenant; see our Dark Souls 2 covenant guide for more information. When you do, you must kill 50 players while wearing the Crest of Blood ring to receive this.