Borderlands 3Shield Pool

Borderlands 3 World Drops are items that drop from any suitable Loot Source in addition to their dedicated sources.
There are around 150 unique items in the Base Game - World Drop pool, so for farming a specific shield it's best to seek out its dedicated Loot Source.
If you still want to test your luck, you should equip a Shlooter Artifact or All-in Shield to increase your Legendary World Drop Chances.

Shield - suitable Loot Sources:

• All Enemies:
  Bosses, Crew Challenges, Generic Enemies, …
• All kinds of Chests
• Vending Machines
• Slot Machines: Tink's Hijinx or Vault Line
• Diamond Loot Room