This is a particularly tricky one. You may need to try records in the UK, South Africa or even Argentina in order to get more clues about this particular relative.
However, some other sources that you may try include: Civil registration records which are available from the General Register Office (GRO). These start from 1864. You can access the website here: http://www.groireland.ie/research.htm Some other websites that may help are: http://www.rootsireland.ie/ifhf/map.php for information on the Dublin area or https://familysearch.org/ and also http://www.irishgenealogy.ie/
I wish you the best of luck in your search.
Please make sure you link anyone else in your family who is interested in their Irish heritage to our site - and indeed anyone else you know of Irish heritage.
Ireland Reaching Out