Help with Galaxy S3 update

I have an AT&T Galaxy S3 that I had unlocked after paying AT&T and getting the unlock code from them. My device is on Android 4.1.1. I know that the 4.2 update has been released for the phone but it does not show up when I check for the update or on Kies. I am using the phone in India and cannot contact AT&T. Is there anyone who is in a similar situation or can help. Thanks.