The Murphy Bros wagon did exist, have seen a builder's photo of one in New Irish Lines a good while back. Never seen one elsewhere though, so must have been either very short-lived and bought out by the GSR or whoever and painted grey like the rest or become so filthy and neglected that the wording couldn't be seen.
The Kilkenny Coal Co, like most of Hornby's Irish interpretations, are pure fiction.
The only other bona fide PO wagons from days of yore that I can think of off-hand are Ranks grain wagons, Mex/Irish Shell etc. oil tank wagons, Lyons Tea and Denny's containers.
Think there were Guinness wagons, not a lot it would seem, there's a pic of one in Achill in the 1890's/1900's in Rails to Achill by what's his name and I *think* the RPSI had a bogie version?