Din't give up hope just yet. Civil registration of births, deaths and Catholic marriages did start in 1864 (only from 1845 for non-Catholic marriages) but there are some earlier R.C. church records still in existance.
CAVAN RESOURCES has a link for R.C. records-
www.from-ireland.net/cav/cavanrcindex.htm Luckily Shercock R.C. records look quite good although they don't perhaps go back as far as you'd want-
Killanne (Bailieborough - Bailieboro, Shercock)
Baptisms: Jan 28th, 1835 - Nov 20th, 1849, Jan 13th, 1868 - Nov 19th, 1880
Marriages: Jan 12th, 1835 - Feb 12th, 1850, Jan 28th, 1868 - Sept 22nd, 1880
National Library (Dublin), PRONI (Belfast) and LDS seem to have copies. If there are available elsewhere someone else is bound to post the details here for you.
You might also want to look through the other links on the RESOURCES thread-
www.rootschat.com/forum/index.php/topic,411564.0.html