Pauline,
I'm no expert, but I think your best bet is civil registration rather than church records (though I have also found marriages in newspapers - especially useful before registration).
LDS have parish register films for Dundalk, but the marriages end in 1803 for the Church of Ireland, and 1831 for the Catholic Church. I don't know why in this case, possibly the later ones destroyed in 1922?
Civil registration (in theory) covers all marriages from 1 Jan 1864 (Catholic marriages excluded before then). See the GRO website
http://www.groireland.ie/research.htmBy mail, you can order a photocopy (rather than a certified copy) for only €3.80 but only if you have the names and the date of the marriage. See the application form at
http://www.groireland.ie/apply_for_a_cert.htmIf you were in Dublin you could use the indexes in the GRO - but I guess that's not an option.
Fortunately the LDS have indexes. If your local LDS FHC do not have a permanent set of indexes (worth checking), you can order the films in. Not all of them though, there are 334 films in the set.
The link to this humungous and possibly session-based, so I won't try to post it; bit it's fairly easy to get there from place search:
http://www.familysearch.org/Eng/Library/fhlcatalog/supermainframeset.asp?display=generallocalitysearchenter "Ireland", select "Ireland" (top of list), then select "Ireland - Civil Registration" on the 2nd page of topics.
Then on that page, select
Marriage records, 1845-1870, with indexes to marriages, 1845-1921, in the General Registry Office of Ireland
You'll notice this actually has the records to 1870, but even so you'll still need to check the index if you don't have dates, as there are many films to a year.
Go to "View Film Notes" as usual - here are some of interest:
Index of marriages 1869-1872 FHL BRITISH Film 101251
Marriages v. 1 1870 FHL BRITISH Film 101555
Marriages v. 2 1870 FHL BRITISH Film 101556
...
Marriages v. 19-20 1870 FHL BRITISH Film 101571
I have never used these films, but they seem to fit the bill.
On the other hand, maybe there's a pay-per-view or subscription index around somewhere? Might be easier.
Steve