Joel,
There are several listed in Sellers that could be a possible match.
#1.) Thomas, J. Washington County, Virginia. Fullstock Percussion, KRA 1976
#2.) Thomas, J & Son Centre Ohio, 1849-1854. Fullstock Percussion .
#3.)Thomas J.M. Eldertown Pennsylvania, 1882d-1885d.
Number 3 could be your man. Its an attractive rifle.
Buck