Hello Kathryn, welcome to Ireland Reaching Out, there is no local volunteer in the area, I live about 40 plus miles away but have some knowledge of the area, was actually there today. Not sure what you are aware of since your last visit but there is a website here and some Carville photos in it too, mostly the same people but a good few photos. No Casserly and one McGivern.
https://www.carlingfordpeople.ie/ There is a site here for Louth but only 2 Carvill hits http://jbhall.clahs.ie/ no Carville so the name is unusual. The 2nd hit is a donation from St John, New Brunswick, I learned from a previous poster that there was a lot of migration to there from Omeath 1820 to 1830s, a gentleman actually told me a book had been written on the matter, out of print now but he had sent a copy to Dundalk Library (main reference library in Louth) the title escapes me though. Another gentleman who proposes to visit in October tells me there are a lot of graves in New York state again forget the place of Cooley people but if you wish I can ask him as we have occassional exchanges of email. The chat should turn up under Omeath parish, you could also post in the Chronicles section.
As well as the Carlingford website above there is a Facebook page Louth genealogy, private group but like all these FB pages answers can be short but occassional gold.
The Louth Liberary and Archives may be worth mailing but it is nearly impossible for a variety of reasons to go beyond the early 1800s as the only available records are churh records pre 1864 if they exist. You can see when records commenced here https://registers.nli.ie/parishes/0194 so 1835 is the earliest baptisms shown.
The Louth Library mail is here https://www.louthcoco.ie/en/services/library/genealogy-research-sources/ and archives are here, also in Dundalk. https://www.louthcoco.ie/en/services/archives/
Hope that is some assistance to you, please revert if you have any queries and I will endeavour to assist.
Regards
Pat