If you still have the numbers the dealer can cut you one. If you know where the vehicle was origionally purchased some dealers have the info. on file. Other than that you hace to replace the lock cylinders or at least remove them and take them to a good locksmith and with luck tyhey can cuut one for you.
* If you have the vin number ( located on the dash on the drivers side and seen from the outside of the windshield looking into the car at the bottom of the windshield or on the sticker on the door seen when the door is opened and looking at the width of the door or the door jam.) the dealer can make a new key with this number and often a lock smith can as well.