Hi - the only comprehensive published material for marriages in Snyder County does not go back as far as you need. The Wagenseller marriages book starts about 1835. Dr Charles Fisher's book has earlier records, but I don't find the Kelly you name. His work includes several preacher's records (they worked curcuit charges in those days), and several unsourced "miscellaneous" records. The only thing I could suggest is the LDS library for church records. Sort of a long shot, but if you know where they lived, and what denomination they might have been, the older church in the area may have something. You can find what they have available by using their library index on-line. You should also check with the Snyder Co Historical Society; their collection has become very extensive over the years.