Being from 'not Dublin', I'll second the Homebrew centre in Clare. Until you go All Grain, they have most stuff you need, and even then they can order in items not on the site. very helpful people.
Of course, if you know someone in Dublin, then G'n'G could deliver to them.
The guy in Cork is Bob from Glengarriff. Do a search on this site, as he's been mentioned before. A quick phone call and he'll post out a catalogue. If you don't have any joy I have his number at home somewhere.
There are several UK based sites, as Oblivious mentioned. I also use Hop Shop[/url:wka8v4in]. Mainly for lighter items, yeasts etc.