I didn't find a Thompson family in Spotsylvania County in the 1810 census or the 1813 taxlist, but Betsey Thompson was listed as "M" in the 1813 personal property tax list for the City of Fredericksburg.

Westmoreland County had 7 "other free" Thompson households listed in the 1810 census.
The Library of Virginia doesn't the register of free Negroes for Richmond City or Fredericksburg on microfilm, but I have heard the the original one for Richmond City is at the archives.
Paul