Just checked on Ticketmaster to see how single game ticket sales went yesterday. The bad news is:

Dallas and Chicago appear to be completely sold out. There are some scattered singles still available for Tennessee, as well as for the Arizona preseason/Green Bay Christmas Eve ticket package (the only way to get a seat to the Packers game). The seat it found for the ARZ/GB game was actually a pretty good one, lower row in the upper deck around the 20-30 yard line.

The good news is:

There ARE still limited tickets available for the games against the Giants, Lions, Jaguars, and Seahawks. Ticketmaster is being sneaky, though. You can do a search for 2 tickets, and it will tell you there are none available. If you search for 3 tickets, however, it will find you 3 tickets together. I don't understand how/why they should be able to do this, but you might be able to go to a Ticketmaster outlet and have them search under the same conditions, but only purchase the two seats you need.