go to any gm dealership and ask for the door and trunk key code. bring proof of ownership. title/reg. they can pull it up with your vin#. if they dont charge over 20 bucks for the new key just get it from them. or take the code and hit up any auto lock smith shop.

you could also buy new locks and keys off ebay. they are pretty simple to change out. but the key code would be the easy way.