Have you tried using the Catholic Church records on familysearch.org.
Assuming they may have been Roman Catholic, I did a quick scan through the baptismal records 1855-1861 of Catholic Basilica of Saint John the Baptist and found two baptisms with Michael Cashin and Mary Walsh as the parents, and who live in St. John's. Here are the links to those entries
https://familysearch.org/pal:/MM9.3.1/T ... :n22944482https://familysearch.org/pal:/MM9.3.1/T ... :n22944482Indexed baptismal records cover from 1802 to 1899 and are easy to search through...marriage records cover from 1799 to 1899 but are harder to search through.
I hope you will be able to use this site to fill in some gaps for you.
L. Moss