They also gave some out at events for fans last year. I got mine from ESO Tavern at Gamescom.
I think the best chance now is to take part in the Torchbug give away each week on Twitter, even if you just create a new account to take part in them.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."
You just follow them, wait until Tuesday, retweet it and they will announce if you win and send you a PM. I actually won one week as I was trying to get one for a friend, when I won it I just asked for the code to give to the friend and they obliged.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."