They appear on the Irish BMD Index on www.familysearch.org at Waterford:
OLIVER McMANUS & MARY BRIDGET THORNBERRY
Waterford marriages Apr-Jun 1925
Vol 4 p 374
Using this reference, the certification can be ordered from teh General Registry in Ireland.
There is also an index reference for the birth of OLIVER PATRICK McMANUS (Oct-Dec 1900) in Tralee.