Is Thomas' father, Martin, the Martin Shewmon born Dec. 28, 1817?If so, are you willing to share more information about the family. I am following the Halderman's and Hannah H. married Jacob Shewmon. They married March 10, 1804 in Botetourt County, VA. Martin is one of the 9 children that I have born to them, but I don't have much on any of them.
Also, have you sent in for a pension application file or military service record for Thomas from the National Archives? Maybe that will turn up something.