The Army of Two GS exclusive code was unique and one time use. I made the mistake of not pre-ordering it there because I also thought it was going to be non-unique and just a generic code.
Luckily, I called them and asked if they had extras and the person who answered was very nice and she gave...
A short while ago, Konami of Japan updated their page, stating that the MGO beta is now scheduled to start Friday, April 25th at Midnight. However, it was stated that this new start date could potentially change as well "due to unforseen circumstances." --IGN
The deal is back and most likely will drop again like last time.
The price dropped to around $23, so keep a look out!
http://www.amazon.com/exec/obidos/ASIN/B000Q36UJQ/