At the moment the most important hxc bands are:
Famine (previously Forging Friendships)
Forced Out (with Matteo who plays in Purification)
Bands that don't exist anymore:
Another Day In Hell
Barntown Water Tastes Like Blood
...sorry, dont remember any more...
The thing is Ireland never had big hxc scene until maybe 3/4 years back. Many of the people were just some indie kids or kids who've been into nu-rave and all that shit but then come hc kids, some were just typical My Chemical Romance fans..sorry to disappoint you..
However there were some kids form bands like Crowd Control, Nelly from Frustration (before he had a band called Barntown Water Tastes Like Blood) who been into hc for bit longer..
I'm sure there are a couple more bands but I moved away and didn't follow that scene anymore, it wasn't my cuppa tea anyway..
If you'd like to get some more info, you should check moshspace. There's Local Music section, however you gotta dig cuz there's lots of shit emo/pop punk bands that have nothing to do with hardcore and only few hc bands..
How could I forget about bands like Find a Way! really good band with nice dudes. I'm not sure if they're still playing but i used to like them alot.
There's also band called Drainland. They're more sludgy, bit crusty hc.
Another one is Tunguska with 2 Irish and 2 Polish members.. I'm not sure if you like this stuff but i think they're really good and played damn good shows.
There was this band called Born A Ghost i think, thats (Frustration) Nelly's first band, it was more like Underoath "emocore" type..