Hi Pats- I
Civil registration only started from 1864 in Ireland. As your dates are before this I'm afraid you would have to try for parish records.(the only exception is Church of Ireland marriages which start from 1845).
If John and Elizabeth were married in the parish of Rockhill Bruree (Roman Catholic-I'm not sure about Church of Ireland)you could write to the parish priest.
I wrote to the parish priest in Rockhill Bruree Co Limerick for baptism details for my greatgrandmother which I received. The records there start from 1825 so you may have some luck for the marriage.
Also you may like to look at this site for Limerick Ancestry -unfortunately they have closed but it still shows the index of records held there.(have a look at the entry above yours- on Rootschat -' Limerick Ancestry Lobby-' it would be good news if it re-opens)
Click on Limerick(shaded green) To find all the Cussens input the surname only. To be more precise input the christian name as well.
You can do the same for Quade, Kelly etc. There are lots of entries for Cussen
https://www.irishgenealogy.ie/csi/csi_main.cfmAlso Griffiths Valuation of Ireland (a valuation of land owned and leased taken between 1848-1864) would give you an idea of some of the Cussens in Limerick at that time.There were a couple again in the parish of Bruree(Rockhill).
(scroll to the bottom-go to Griffiths-select Limerick and input Cussen)
http://www.leitrim-roscommon.com/GRIFFITH/If you write to the parish priest I think it's practice to enclose some euros as a donation in order to defer the cost of time/postage etc. The parish priest was very helpful and the reply didn't take long.
You may also find this site of some interest.
http://www.limerickdioceseheritage.org/RockhillBruree.htmHope this is of some help
Regards
Neptune
