You will want to look for copies of three privately published books on the Bowyers. All three are by Maryetta Francis Bowyer and the titles are:
"The Bowyers of Old Virginia 1607-1979" published by Gray Printing Fostoria Ohio
"Leaves and Branches from Bowyer Roots" publsihed by The Hubbard Co Definace, Ohio Lib congress # 84-91223
"Adam Bowyer Senior of Augusta Co, Va and of Greenbrier and Montroe Counties is West Va."
This is a "family narrative" and contains fairly detailed information on the first Bowyers in Va and their descendants. There are few source notes, so its accuracy is open to some questions, I suppose.
I came across them in trying to learn more about the origins of Joseph Boyer/Bowyer b. Augusta or Rockingham County in 1794. I found no connections and am still looking. If you come across anything, please let me know.
I did notice references in the books to Colonel John Bowyer and to Thornhill. Hope this helps.