Marriages generally took place in the bride's parish if not the same as the grooms perhaps that is why you couldn't locate it.
I'm surprised you didn't find records on rootsireland.ie
as they list Killdorrey has baptisms from 1824-1912 and marriages from 1803-1922!
I'm looking at my map and don't know where the line is between them although I can see Kildorrery 12 mi. from Mitchelstown.
I did find a later Gallagher family from Kildorrey in the civil records CD by the Latter Day Saints, no longer available and replaced by the website www.familysearch.org
I didn't find any Galway's listed in Kildorrey (but other places)
Parents John Gallagher & Ellen Roche
Mary Gallagher born 10 Dec 1870 #859 Kildorrey
John Gallagher born 18 May 1872, Kildorrey
Elizabeth Gallagher born 24 July 1874
These parents would of been born about 20-25 years earlier than 1870!
Sorry I can't be of more help.