I realize you mention the family you are looking for was from North Carolina, however, have you studied the history of The Randolph Slaves?
I mention this because one of the families given their freedom by John Randolph was named Ryal/Rial/Riales or several other spellings.
http://www.tdn-net.com/tdnadmin/tdnhtml/html/rossville/You might be able to find the information you seek at this museum in Piqua, Ohio.
Many of the released slaves went to Piqua Ohio, after being released by John Randolph's will. Remember they were given freedom before the Civil War, and if they had gone somewhere south, (like North Carolina) it would have not gone well for them. Instead, they went to a Quaker village in Piqua Ohio. Some with the name Rial/Ryal still live there.
Cheers,
pcrial