Skiffington family

I have been looking, unsuccessfully, for the place that my great great grandparents came from in Ireland. His name was Michael Skiffington, born in Ireland about 1823. He married Mary Quinn. In 1848 their first child was born in Philadelphia, Pa. I have been unable to find any passenger records on them. Assuming they married in Ireland but don't know that for sure. I have everything I can find on them in the United States, but nothing gives any indication of when they came here or where in Ireland they came from. Has anyone seen this name or is perhaps researching this family? This has been stumbling block for several years. Would appreciate any help given. Thanks
Eileen