I don't know how things work in IReland, but in the US reputable breeders hardly advertise puppies ever. They advertise their kennels in dog magazines and on the club site for the state or country for their breed. As far as their puppies go, they keep a waiting list well before they are born.
Remember with a small breed with health concerns, try for a breeder who keeps them 12 weeks and does not ship puppies. Letting them go too young and shipping are red flags.
Here's a club site you might look into to find breeders
www.thenorthernkingcha.../index.htm
There's a different one that is the Northern Ireland club for cavaliers but the site hasn't been updated in some time. If you look on a dog's championship name if you look up show dogs, the full name usually has the kennel name in it. You can plug the kennel name into a search engine and see if it comes up with anything.