Marriage of Margaret O'Connell and John O'Connor

Hello I wonder if any one can help, I am trying to find the Marriage certificate for my Grand parents please.. I need more Details on there fathers and area they lived mainly. Cant seem to find them on the census. They were married in Ireland 1919 . My Nan was born  20th Sept 1899. I have found her birth certificate but need more information from Marriage certicate. as for my grandfather I cant find any thing, I know he was in the army.  His name was John Joseph O'Connor Born 4th July1892, Died 11th April 1969. not sure what I am doing wrong, I

Any information or a link would be most appreciated.