I use the home brew company shop. Decent selection of products and E5 courier delivery anywhere in Ireland. http://www.thehomebrewcompany.ie/
You can find out more info on the Irish home/craft brew scene here http://www.beoir.org/
In Cork city there is a home brew club that meets up on several Saturdays during the year for brew days in the Franciscan well brewpub http://www.facebook.com/pages/Lee-Brewing-Club/217079661653903
and they are having a home brew expo on June 23rd https://www.facebook.com/events/268943436537180/
with samples of beer brewed by club members and the home brew company on site with supplies for sale.
Also, if you haven't done so yet, pop into Cork city and visit the Franciscan well, the bierhaus, and the abbots ale house. The abbots ale house also has an extensive off-licence and recently received a keg of spelt saison (limited edition brew from trouble brewing http://www.troublebrewing.ie/