Hi Joe -
Riley Marion Byrd's first wife was named Rebecca Gardner; was she perhaps a sister of your Andrew Jackson Gardner perchance?????
Also, I have a brief doc re Forrest's 3rd Tenn. Cav. indicating they were indeed recruiting in the Stewart Co. and Montgomery Co. area in early 1863. There apparently was a "Captain Brewer" doing the honors at that time..??
y.v.o.s.,
Ken