Unless you can get to the National Library in Dublin to view the microfilms for the parish, then it might be simpler to search Civil records for the area. Dún Laoghaire is in the registration district of Rathdown.
The parish records are on films : Pos. 9071, 9072 and 9073.
Some transcript records for the parish are also available on the pay-website of the Irish Family History Foundation at : www.rootsireland.ie
Like many RC parishes Dún Laoghaire/Kingstown didn't record death/burials