Lost keys question ?

My husband lost his keys to his car we looked for them at his job and can't find them he went to work yesterday and When he was about to come home he couldn't find them so anyway we don't have another key that was the only one since we can't find them what do we Do now ? Where do we get a new one ?

We got this car from a used car dealership if that matters and the car is a 2009 Chevrolet Malibu

Does anyone know how we get a new key ?