Mecklenburg had two Registers of Free Negroes -- one dating 1809 to 1841 and the other 1841 to 1865. I'm not sure if originals are in Mecklenburg clerk's office or if at The Library of Virginia. Are abstracted/recorded in Appendix of *Life by the Roaring Roanoke; A History of Mecklenburg County, Virginia* (Bracey). No one with last name of Alexander in either, for what that's worth.