You'll collect these by killing the big stone enemies known as Ancients around God of War's open world. When you kill your first Ancient, you'll unlock a Labor named 'Hearts of Stone'. From there, you just need to give an Ancient's Heart to Brok or Sindri at a shop to unlock the Ancient armor set pieces.

How do you get the Ancient armor set bonus?

Ancient Proficiency is a Set Bonus available from the Ancient Armor Set, which Link can have made for him at Akkala Tech Lab by use of the Ancient Furnace. In order for the Ancient Armor to get Ancient Proficiency, Link must have all three pieces of the set upgraded at least twice at a Great Fairy Fountain.

Where do I get ancient set?

The Ancient Set is an Armor set from Breath of the Wild. The Ancient Set can be purchased from Cherry at the Akkala Ancient Tech Lab.