From Outwar Wiki
Start: Synge Destruction Area
Those Stone-scaled Basilisk's chipped off my other wing, will you get it back?
Solution: Kill stoned-scale basilisks till you reached 27 and by any chance one of them will drop a gargoyle wing otherwise keep killing them till one drop.
Did you get the wing?
Quest objectives: Gargoyle wing: 1/1 Stone-scaled Basilisk: 27/27 killed
Reward: You have recieved 3,000 experience!
Edit: Level I got it 25.