you can sometimes pick up nice paintings at antique auctions. Don't bother with the specialist auctions, just go for one with the most lots on sale.
If it's unsigned or unknown you might pick up a bargain.
Maybe just google irish artists and approach them directly. An artist i know offered me a discount on the website prices and i'm sure they would all do the same. (assuming no agent involved)
I was in Bordeaux last year and there was some amazing original art available at very reasonable prices.
Are you looking to buy it for yourself or a gift or to re-sell?