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.
I've never had any of these fancy coatings, i give the car a full clean half a dozen times a year and find it shines like new anyway. I used to clean my cars ever week with the best of stuff but come trade in they don't care so i don't bother as much nowadays.