The registrar for Gresham was Computershare Investor Services (Ireland) Ltd. I believe that they still hold the 'Dissenters Regsiter (all those shareholders who have not yet accepted the takeover offer and have not, therefore been paid out). Anyway if you haven't already done anything I would suggest you contact Computershare initially:
01 216 3100 (make sure you tell them that it is a taken over company as they may have difficulty locating)
Computershare Investor Services (Ireland) Ltd
Heron House
Corrig Road
Sandyford Industrial Estate
Dublin 18
PS: If I recall correctly, the old Ryan Hotels share certificates were still valid at the time of the takeover.