Vicki, compulsory registration of marriages didn't come into Ireland until 1845 for
non-Catholics and about 1862 (I think) for births deaths & marriages for all people in
Consequently all you could expect to obtain would be a copy of the Parish Register when
your ancestors married if same exists. Otherwise I guess all you could get would be a
copy of an index.
You can search on PRONI for all the information available for the parish of interest -
PRONI Guide to Church Records.
Margaret in Oz.