Glovebox, ashtray, in the jack kit, at the garage of purchase, still on the nut, lol. Could be anywhere! You can get them smashed off for £40 or try yourself by either drilling a slot into the nut and removing with a screwdriver, big muscles needed or find a socket the closest size and hammering it on the nut, NOT a good idea.
Best take it to a garage and get it sorted, if the garage you bought it from didnt supply it then its their job to find it or remove the locking nuts and replace with new.