I couldn't find it either so i made one. It is basically blues in A, but capo 2nd fret and play open G chord, etc.
here is great youtube clip of doc playing it.
http://www.youtube.com/watch?v=YzRCdKbtBYo


Southbound
Merle Watson
Capo 2

I've been here a month or more stuck in this ol' city
People that have to call it home, they the ones I pity Lord I'm homesick
and the blues are the only songs I ever seem to pick
I get out and walk the streets
'til I get blisters on my feet
I'm southbound

I'm all right 'til late at night sittin' by my window
I count sheep but I can't sleep listening to that train blow, I begin to pine
When I hear that great big engine rollin' down the line
Listen the engine rattle 'n roar
She's gonna take me back home once more
I'm southbound

Southbound she's burning the ground
and I don't mean maybe
Sure am glad I caught this train
Cause I'd like to see my baby
Lord I'm lonesome
and I long to see those hills that I come from
I'm goin' back to spend a little time, where a friends a friend when you ain't got a dime
I'm southbound