I just did the same thing with my 07 QP. You have to order the key from any Maserati dealer. The key costs about $300-$350. You will have to provide them with all sorts of proof of ownership, etc. to get them to order it for you.
They cut the keys in New Jersey and you will get it in within a week... You then need to pay the dealer to reprogram all sets of your keys (two then in your case). They charge between 1/2 and 1 hour for this. Be sure you have your electronic code from your owners manual pack or it will cost you another $100 for the dealer to retrieve your electronic code from FMNA.
Lock and unlock the car quite a few times. Initially each time you press the button the indicator lights will flash and the red alarm light will come on. Eventually one of these presses will not make the indicators flash and just the alarm light will come on. The car is now in learn mode. While in this learn mode you must click all the keys that you want the car to respond to, otherwise you'll be in the same situation again - but with one of your blue keys.