Marjorie said this morning they arrived at Castle Garden, on the southern tip of Manhattan which preceded Ellis Island. This may not be true--from what I can see by Google it wasn't an official entry station until 1855. But here's its web site and here's Wikipedia.
And you can search the site for immigration entries going back to 1820. Unfortunately, the first Harshaws included in the database didn't arrive until 1848 (Samuel), with a large group on July 2, 1849. (A "James Harshow" did arrive in 1834.)
Here's a list of pictures of the potato famine and emigration, including Castle Garden ones.