The subscription site Roots Ireland has a number of John Leahy baptismal records ( with father John) in the 1830s, none in 1840-1842 and then there are two 1843 records and one in 1844. The one in 1844 is the only one in Kilmallock parish.
February 12 1844 Kilmallock father John Leahy and mother Ellen Gubbins.
The Kilmallock records start in 1837 and Kilfinnane start in 1831 so it will be difficult to go back further.
Not sure if the record above is correct but possibly the father John Leahy is a brother or cousin to the Patrick Leahy born around 1806.