There's no one website to keep track of upcoming airdrops. The best strategy I've seen so far is to be a part of a community where latest information about such events / announcements are posted by other members. This way you won't be a lot if you're active as there are most eyes on new opportunities and announcements as they become available. You should get onnit asap as more drops might be on the way —see zksync and layerzero (heavily rumored in recent times).