It is done at the dealer, often by a local contractor. No doubt there are differing opinions on this but I have been warned more than once by those in the car sales business that these coatings are simply a way of "adding value" i.e. extracting more dosh from the customer.
I have only had one car coated in this way and it was a complete pain in the arse. It wouldn't polish up properly and wouldn't come off either.