Someone on Reddit had indicated they got the holographic dragon wing skin from an ogre they killed. Not from a dragon coffer box but a mob they killed. So, probably from doing our own thing while the event is up may net us pets and skins off of just about any creature we beat up is my guess. I'm not saying go out and grind. Just keep doing what you're doing and you will get something at least.
This seems more reasonable than farming tons of candy nonstop but for the obsessive player, I'm sure they will feel it rewarding to buy the wings from the vendor. I've seen some players with the wings and HG said that some players simply spent gold on candy in the TP. I'm thinking others may have gotten them as drops in the world as well.