The Travel Reference (VA) US 58 RR Wiki page lists 211 Buck Mtn as the tower that covers Mouth of Wilson. You might want to try that first. If that doesn't work for you, as suggested above, you might want to try 210 Whitetop Mtn which covers west of MoW, and then 209 Beamer Knob which covers east of MoW.
Yes good advice on the Buck Mountain, that should come up. It wasn't an original STARS site but added later. It covers from the I-77 tunnels in Bland to south Grayson County.