I'm not Irish but I live in Dublin. As far as I know Blake and I are the only active cubers in Ireland. I live in Dublin and he lives in Galway.
Anyway I'm far too busy these days so I don't think I'll have any time cubing until the end of May. Blake seems to be quite busy too.
There are some other random Irish cubers who occasionally appear here, WCA forum or TwistyPuzzle, but then they just disappeared and never show themselves again.
The best choice for a competition is go to the UK where 2-4 comps are held every year.