Umbral Chains

Key Uniques

Here are the important uniques for this build and where to farm them:

Scourge of Duriel (Warlock Flail)
This is one of the core uniques. It increases the damage of Umbral Chains and adds an extra variant to it.
Best farm: @Duriel (as the name suggests). You can also target it using @Duriel boss trophies in the Horadric Cube.

Footfalls of the Waning World (Boots)
This is probably your highest priority unique to farm. It gives you extra Evade charges or reduces Evade cooldown.
Best farm: Complete Escalation Nightmare Dungeons. You can also target farm it by running bosses and then selecting the Star option that drops loot from Escalation dungeons.

The Hemat Stone (Amulet)
This is another strong unique for the build.
Best farm: @Bartuc, Lord of Chaos (from Infernal Horde). You can also target it using @Bartuc boss trophies in the Horadric Cube. It can randomly drop from Helltides and Nightmare Dungeons too, but Bartuc is by far the best way.

Godslayer Crown (Helm)
This is a great item if you want more crowd control. It pulls enemies in and groups them up nicely, which helps a lot with Umbral Chains.
Best farm: @Andariel is currently the strongest target for it. It can also drop from @Duriel.

Speed Farm Version

Banished Lord's Talisman is another strong unique amulet you can consider for this build.

It gives a big boost to Overpower damage and makes your Core Skills hit significantly harder after you spend a certain amount of resource. It’s especially good if you’re already scaling overpower in this version of the build.

Unfortunately, it no longer has a dedicated target farm. It was moved into the general unique pool, so it can drop from pretty much anywhere in Torment difficulties — Helltides, Nightmare Dungeons, Lair Bosses, etc.

Mythics

Two really good Mythic uniques you can use in this build are Heir of Perdition and Tyrael's Might.

Both can be found from any of the Greater Key bosses. The easiest and most consistent way right now is farming @Belial, but they can also drop from Tormented @Duriel and @Andariel. Mythics can technically drop from most high-end content, but these bosses give you the best chances.

Runes

I’m running two rune setups here.

The first one is Cir + Ceh. This summons a Spirit Wolf that attacks enemies, and it also applies freeze and Vulnerable at a really good rate. Since Warlock doesn’t have many easy ways to apply Vulnerable (outside of the Sentinels), this rune pair is a really nice addition. The wolves also act as good bait, which helps a lot.

For the second rune setup, I’m using Cem + Que. This one lets you summon Earthen Bulwark, which gives you a big barrier. It’s a solid defensive option that helps with survivability.

These two pairs work really well together for both offense and defense without feeling too clunky.

Early game you can use Mot as alternative to Que.