I'd tell them where to shove their lock nuts, they shouldn't have taken them off without the key, probably the wet behind the ears apprentice doing all the grunt jobs.
If they're a major chain you can complain to the franchisor, that is poor form on the tyre shop's part.
You didn't have the lock nut key with you in the car?
Don't bother with the nissan dealer, they'll just overcharge you. Get a new set of lock nuts & keep the key in the boot or the console. Like I said you can try supercheap/autobarn as at least they're open on sundays. Loosen up one of the factory nuts when you go to a shop & they can find a suitable type