I'm a descendent of John McGarry and Elizabeth O'Flynn, through their son John J. and his wife, Blanche. I can get info from my grandma for this line.
As far as information going further past John & Elizabeth, we have the boat name/number they came from Ireland on, but we can't go any further back as it appears their name was changed to McGarry upon arrival at Ellis Island. We know the towns that each was from, but we don't know what their original last names were before they left N. Ireland.
My grandmother would definitely be interested in that information if anyone had it.