Hi Brian,
Great question! Actually I think the reason it is hard to find such references is mostly that swords of Ireland and Wales are often grouped into larger headings, for example those Irish examples appearing in "Scottish Swords and Dirks" by John Wallace, 1970. I suppose a lot in answering this would depend on more specific circumstances and periods.
References which show Viking and Frankish swords include weapons from Ireland as well as Britain. Naturally Scottish and Irish swords, as noted, are often intergrouped. The mercenary warriors known as 'Galloglaigh' of 13th-16th centuries used swords in these kinds of mixed category.
The Journal of the Arms & Armour Society (II, #1, 1956) is focused on Irish arms and armour.
"Sixteenth Century Irish Swords in the National Museum of Ireland" by
Gerard Anthony Hayes-McCoy, Dublin 1959 (1977)
"Irish Medieval Swords 1170-1600" Andrew Halpin ,
Proceedings of the Royal Irish Academy, 86 C #5,
Dublin Royal Irish Academy, 1986
These are among the number of references on Irish swords. Again,depending on period, other categories might also be applicable.
On Welsh swords, naturally the swords of the Romans such as the spatha come to mind, and later Anglo-Saxon swords would be the best sources.
"The Sword in Anglo-Saxon England" , Hilda Ellis-Davidson 1962 (1994) is an amazing reference with illustrations by Oakeshott, and gives a good overview on swords that would fall into the headings including Wales and Ireland.
In MAN, May, 1931, there is the article "Discovery of a Saxon Sword in Wales" by C.E.Vulliamy, describing this exacavated weapon.
Naturally the swords of these countries from the 18th century forward would be among those of Great Britain. With that being the case and regarding regulation swords, these would be researched accordingly with unit and military histories.
Hope this will be of some help
All the very best,
Jim