Two expansions were added, Sudden Death in 2013 and Foul Play in 2014. However, with GW taking back their license those expansions became much rarer. Sometimes they pop up and usually run in the $70 USD range used.
A group of gamers on Boardgamegeek have worked together and using Table Top Simulator for beta testing have began to release fan created expansions. The first season of which is now available.
The new expansion teams, Elf Union, Norse, Khorne, Kislev, Ogre, and Chaos Renegades. Having played with the new teams, I must say they integrate seamlessly with the existing game. The quality of the artwork and cards is quite professional. I had a set professionally printed for myself.
If you bought the game years ago and missed out on the official expansions, or if you want to refresh you current roster with some new teams, I encourage you to give them a try.
Here is the bgg link with the discussion, the printing links are updated within the thread.
Also, if you are interested in helping with the playtesting, some of the beta work for other teams is located here.
Here is a photo of some of my expansion cards just so you all can get an idea of the quality:
