Picked it up for fairly cheap and got a free t-shirt with it too. Haven't played it yet and won't until I'm done with Uncharted 3 however.
Sorry to hear that you are having problems with your Moonraker Laser Pistol.
If your content is not working, your best bet is to give the PlayStation Support Centre a call so we can have a look to see what might be causing this issue.
Would you please be able to confirm where you are attempting to use this item? As far as I am aware, the gun can only be used in multiplayer and when using "Hugo Drax" and believe it is unlocked at level 8.
Let us know how you go.