If you are lucky there is a key code in the owners manual (I was not lucky) and a dealer can cut you a key with the code and proof the you are the owner of the vehicle. I was also informed that the code may be on the door lock cylinders but that requires removing the interior door panels (no guarantee). Otherwise you can try to contact Porsche with the VIN and a bunch of money and they may be able to research the code for you - once again no guarantee. I do not know if a locksmith can rekey. Good luck and let us know how this plays out for you.
Carl