My only suggestion is to call Ziggy's Feathered Friends (Dorchester, near London) because I've seen Kelly (owner) offer Ringnecks for sale when I've visited previously.
Beyond that, I don't have personal experience with any, but I just checked the Parrot Breeders Canada group on Facebook and a search for "ringneck" shows a few results in the Golden Horseshow region. You may want to inquire there if you don't find a better recommendation here.