Howzit and welcome.
Can you see a brand name anywhere on the towbar? It looks to me like a brink system. So maybe try giving them a call or a Thule fitment center. Google is your friend. I'm not sure which branch will be closer to you but they are all over. You will just need the number written on the lock (G508 by the looks of it) where the key goes in and they will give you a price.
PS. Don't forget to start an intro thread with some pictures of the beauty. Before there's some trouble.
Regards.