I was looking at these trucks in January. I was able to find a good number of them. I also found the max tow with the 5.3. I then decided that I was not going to sell my 2500HD.
As for Don's comment, this was not the case. When GM announced the 6.2 and max tow, they indicated that it would be available in Q4 2013. They were available in Q4.
Jimbee - Some dealers will work with you on a specific order. You can always ask a dealer if they will sell you a special-ordered vehicle at the GM Supplier and Friends price. If they will, you can ask a GM employee for a Friends price certificate.