Lost keys

Your best bet would be to have an automotive locksmith come out. They will ask for ID and proof of ownership, then make a phone call to the factory and get the key code. From that they can cut a new key and program the system to accept it. This lets you use the door locks and all the rest that you would also need to change with a new key. The same option exists if you had a dealer do the work, but most times the smith will come to you instead of needing to get the car to the dealer.
Replacing the cylinder is an option, however you would still need a dealer level scan tool and the vehicles PIN to get it to accept the replacement keys.