Tony, I will give you the bad news first, Ireland is not a great hunting ground for photographic equipment the market is quite small and a lot of the film photographers would buy in the UK.
The west coast from Galway to Donegal is perfect for landscapes and seascapes. You might also include Clare which is a little south of Galway as it includes The Burren a limestone landscape full of photo opportunities especially this month if you would like to take some wild flower photographs. Working your way up the coast some places worth visiting are:- Burren, Achill Island and the Mayo coastline, Maam Cross, Salthill, Doo Lough, Aran Islands. A few images from these places are on my Blog I have done very little in Sligo and Donegal but I have seen some really rugged landscape images from Donegal.
Make sure you bring a good supply of film as the west coast would have very few shops that supply film.