Go to the Underground Crimson or Underground Corruption in Hardmode
Find a wide open area with enough space to move and fight
Use Battle Potions and Water Candles to increase spawn rates
Equip strong mobility accessories to avoid Pigron charges
Use ranged or piercing weapons to hit multiple enemies safely
Build a flat farming platform with walls and traps if desired
Keep a safe box or arena for healing and item collection
Kill Pigron quickly before it closes distance
Repeat in the same biome until you get the drops you want