A guiding principle of Irish genealogical research in the U.S. and Canada is to exhaust all records on this side of the Atlantic to find the place of origin in Ireland. However, there are two main types of records, created in Ireland, that are also suitable to use. One is certain passenger list records created in Ireland, such as those highlighted by the work of Irish genealogist Brian Mitchell. The other is assisted emigration records. They are useful because the place of origin is given as well as the port they arrived at in North America.
Jim Rees has written extensively about this migration and you can read about it in his document, The Surplus People. He has also compiled names of migrants from the townland of Coolattin on the Fitzwilliam Estate.
 Rees, Jim. Fitzwilliam Estate Emigration Books, 1847-1856. Provincial Archives of New Brunswick, available online at http://archives.gnb.ca/Irish/Databases/Fitzwilliam/Default.aspx?culture=en-CA: accessed 22 August 2013.