As mentioned yesterday, EBGames.com stated that the shipping date for the Xbox version of Mortal Kombat: Armageddon was set for today. The product page over on EBGames.com shows that the game is now in stock and is currently shipping. A quick check of local GameStop and EB Games stores confirm that the game is expected to be in stores tomorrow (October 12th).
Initially, the Xbox version was delayed one week after the PlayStation 2 release. Check with your local stores tomorrow, by calling before you head out. If you are successful in getting your Xbox copy, post a message in our Mortal Kombat: Armageddon Forum.