I needed 4 of those to craft protas trousers
From the Ellomago monster in the “Owl Burial Ground” map, with a 10% chance.
Source:
How can get a lv 109 material for a lv 40 equipment when I am only lv 45
ToS logic. You could get a higher leveled person to farm it for you since it’s a common drop, or check the Auction House for the materials.