[H] Hearthstone Beta Key [W] TF2 Key, Offers

this is probably a stupid question but im new to steam where do you buy tf2 keys

Have: Musaic Box Steam Game
Greed: Black Border Steam Game
Larva Mortus Steam Game
Space Trader: Merchant Marine Steam Game
Saira Steam Game
Project Aftemath Steam Game
Men of War: Condemned Heroes Steam Game
Knytt Underground Desura Game

All these for beta key.

Anything here? I've also got Natural Selection 2.