The following two articles may be of interest to you:
Poul Holm, "*The Slave Trade of Dublin, Ninth to Twelfth Centuries*
in _Paritia_ 5 (1986)
John S. Moore, *Domesday Slavery* in _Anglo-Norman Studies XI:
Proceedings of the Battle Conference_, 1988, ed by A Allen Brown
Each of the following works deals with the subject of slavery in the
west. Although they may not necessarily refer to the practice of
slavery in Ireland, they provide arguments you may find helpful:
Jean Bonnassie, _From Slavery to Feudalism in South-Western
Europe__ Past & Present (Camb), 1991
Pierre Dockes, _Medieval Slavery and Liberation_ U Chicago, 1982
Wm Phillips, _Slavery from Roman Times to Early Transatlantic
Trade_ U of Minn, 1985
Ruth Karras, _Slavery and Society in Medieval Scandanavia_ Yale,
1988