Walsh Family in Lusmagh 1810 - 1830?

Good morning! 

I was hoping that someone could point me in the right direction. Patrick and Honora Walsh had one son born in Lusmagh -- Martin Walsh, born 1813 or 1814, according to two sources. 

I have searched through the digitized parish registers, but it appears that Lusmagh registers begin in 1828, which is too late for the family I am searching for. Are these all the surviving registers, or is there a chance that the older registers still exist within the church? Are there any other records that I should be searching to place the family in Ireland? I do have a subscription to Roots Ireland, but my searches thus far have come up rather empty handed. Although, I have compiled a small list of possible results. The family likely emigrated around 1830 and it is possible that they didn't arrive all at once. As the story goes, they were recruited by someone and indentured, but I am aware that the likelihood of finding documentation of something like that is extremely slim.

Upon arrival in the U.S., the family appears to have been involved with the construction of the C&O Canal and after settling in Harpers Ferry, West Virginia, worked in the surrounding limestone quarries as quarrymen or boatmen, boating the limestone up the C&O Canal into Georgetown. It is my understanding that this area in Ireland is rather rich in limestone, as is other areas in County Offaly near the banks of the Shannon. If I wanted to learn more about both the canal and the limestone industry in the area of Lusmagh as well as County Offaly in general, are there any sources that I should look for first?

Not sure if this is helpful, but if so, we are aware of the following children of Patrick and Honora (b. abt. 1790):

1. Martin Walsh, b. Lusmagh 1813 or 1814; d. September 18, 1855 in Bolivar, West Virginia, USA. Spouse unknown; One known child.
2. Mary Walsh, b. Ireland ca. 1817; d. aft. 1871 Washington D.C., USA. Married Dennis Dunn; two known children.
3. Patrick Walsh, b. Ireland ca. 1820.
4. James Walsh, b. Ireland ca. 1828; d. February 27, 1871 in Bolivar, West Virginia, USA. Married Margaret ?.
5. Thomas Buchanan Walsh, b. Virginia 1832. Married Annie Gertrude Murphy. 8 known children.

Known to be of the same family but are not the children of Pat and Honora are also:

1. Ann Walsh, b. Ireland 1834
2. Pat Walsh, b. Virginia 1838
3. James Walsh, b. Missouri 1858

Thank you so much for any direction that anyone may be able to provide! 

Kaila