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.
Good luck!