How much of her pedigree have you got in your horse's passport? Sometimes its easier searching for grandsire first, as if he stood in Ireland there will be a record of him, and also possibly of his offspring. Try the Irish Horse Board website - they have brood mare books that you can search; alternatively if you email/write to them they ought to be able to give you further information on her if she's an ISH.
Good luck! I had to do the same thing for my ISH filly's sire, and when I eventually tracked him down discovered that he was the most lovely hunter who had led in the hounds for several years at Dublin Horse Show!
Knockboy her sire is an RID stallion, his breeding can be seen on the link below, He is the sire of Sea Crest who in turn is the sire of Cruising. The earliest IHR approved stallion book I have is '95 and he is in the list of deceased stallions but it does not say when he died. He sired 94 registered foals.
If that's Romeo then you've got his dam's owner's address there (Liam Gorman) so maybe you could write.
My mare's dam was covered by Orbis the same year. Our horse's dams may have been at stud together, dunno how it works in Ireland, if they stay for any time or just get covered and go home.