Not sure about Ireland specifically, but any bike shop should be able to help you, or if you can change your own tires, the internet.

LOTS of options out there. I used a 1.95" wide version (strictly because that is what the local sporting goods store stocked) of these when I had mine setup strictly for pavement: Kenda Kwest High Pressure 26" Tire > Components > Tires > Pavement Tires | Jenson USA

Once you get rid of the knobbies and cut down on the width, a MTB is quite pleasant to ride on the road. I got caught up riding mine in a group ride of road bikes on the local path this spring, had no problem keeping up.