O’Shea/ Gallagher Marriage

[MBW]

I am searching for the marriage of my 2xG Grandparents John O’Shea and Ellen Gallagher in Ireland about 1956/7. John was later known as John Nugent O’Shea. His death certificate is under that name. Ellen died in 1894  and John died in 1899. He had remarried in 1896, her name was Eliza Catherine Judd.
Ellen and John had 5 children, Mary A (1858). Ellen (1861). Laurence (1865). Bridget (1867) and Johanna (1869), known as Jane.
Would love to find Ellen and John’s marriage but have no idea where in Ireland they are from. All the children were born in England, around West Ham.
I hope someone can help me over this brick wall.