Without looking at any census info, I'd say it's a sure bet most would live in Dublin. They'llk want to live near fellow Seikhs and religious facilities - which in Ireland would suggest Dublin.
Ethnic and religious minorities do tend to cluster in certain small areas - you know this yourself from living in England (e.g. Southall, Blackburn, Bradford, Leicester, Stamford Hill, Tower Hamlets, Stockwell, Brixton etc etc etc ) sure, the Irish were no different in The Bronx, South Boston, Kilburn, Cricklewood etc etc. So it should be no suirprise to you if, by chance, there was a town somewhere where the majority of Ireland's Sikhs lived. It's the same in England with Southall.....