You can get some team fortress 2 hats for free from other free games easily as promotional items. I am only talking about free games but if you want to know about all the promotional items for TF2 you can check them here.
PROMOTIONAL ITEMS FROM FREE GAMES
1. Alien Swarm
ITEM : Alien Swarm Parasite
Obtainable by Achievement :
Hat Trick
Complete 2 co-op missions online. Earns a Team Fortress 2 parasite hat.
ITEM : Spiral Sallet
Obtainable by Achievement :
Mission Accomplished
Reach the first Clockworks Terminal.
