Purcell-Duggan

I am looking for any information on Edmond Purcell and Ellen Duggan. Their tombstone (erected by their son in Newfoundland) stated they were from Tipperary County. It also stated they were born in the 1780's (the stone is no longer there so I am grateful someone transcribed it before it crumbled away. However, I can't guarantee the dates if it was in that bad a condition). The first mention of them is in the St. John's parish records in Newfoundland when their child, Ellen, was born in 1820. The parish records for the previous 15 years show no Edmond Purcell or Ellen Duggan or any marriage of them. I have to infer they were married in Ireland and left sometime before 1820. I know Tipperary County is a VERY large place to look but I don't have any other information. If anyone else is researching them or has any information, please let me know. Thank you.