I'm not aware of any cruise line offering much in the way of cruising to Ireland, let alone cruise & stay.
Both Princess & P&O make stops in Ireland (Dublin, Belfast, Cobh for Cork, and, Waterford) en route to other countries. It maybe worth seeing if you can get a flight into ireland for a few days, then joining the ship when she arrives, the flying back to Ireland (or the States) after the cruise.
I really don't think that there's any other options (at the moment).
Last: Oceania Nautica Aug 2016
Next: Cruise Maritime Magellan Nov 2016
Then: P&O Oceana December 2016
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