You can buy the game from the Steam. But if it's not your style - you don't have to. There are a lot of cracked servers (e.g. CrackedVodka), so you can just download the game from torrents. Most of them have "Cracked" in their title, so you can easily find them.
But notice that some servers have 1.0 version and some have 1.3 version, so maybe you should install Version Changer to change your game versions.
During install you have to insert game cdkey, so you can take any of this list.
Have a nice game!