The Prince Edward Island Genealogical Society (Canada) and its members have been very active over the years when it comes to compiling publications that can aid Irish genealogy research. They have compiled two publications of Irish genealogy records along with a considerable collection of headstone transcriptions from Catholic cemeteries and those of other denominations.
Gallant, Peter and Nelda Murray. From Ireland to Prince Edward Island : a list compiled from newspapers, obituary notices and cemetery transcriptions of (some) immigrants to Prince Edward Island, from Ireland. Charlottetown: P.E.I. Genealogical Society. 1999.
Gallant, Peter. An index of Irish immigrants based on obituaries and death notices in Prince Edward Island newspapers, 1835-1910. Charlottetown: P.E.I. Genealogical Society. 1990.
A good introduction to the topic of the Irish in PEI is provided by O'Grady, Brendan. Exiles and Islanders: The Irish Settlers of Prince Edward Island Montreal: McGill-Queen's University Press. 2004.