Here's more info from Folk Music - An Index to Recorded
Resources:


Johnson's Old Grey Mule [Me II-W21] - Westendorf, Thomas P.
At - Thompson's Old Gray Mule ; Yodeling Mule
1. Pound, Louise (ed.) / American Ballads and Songs, Scribner's, Sof (1972), p213/#103 [1916] (Old Gray Mule)
2. Blevins, Frank. Devil's Box, Devil's Box, Ser, 32/2, p17a(1998) [1931ca]
3. Ensign, Bob; and the Stump Jumpers. Mountain Guitar Pickin', Rural Rhythm RRBE 255, LP (197?), trk# B.09 (Johnson's Mule)
4. Fox, Curly. Champion Fiddler, Vol. 2, Rural Rhythm RR 252, LP (196?), trk# 6
5. Georgia Yellow Hammers. Moonshine Hollow Band, Rounder 1032, LP (1979), trk# A.05 [1927/02/18]
6. Greer, Jim; and the Mac-O-Chee Valley Boys. Stars of the WWVA Jamboree, Rural Rhythm RRGreer 152, LP (197?), trk# A.09
7. Johnson, Earl; and his Clodhoppers. Red Hot Breakdown, County 543, LP (1976), trk# A.04 [1927/02/21]
8. Mainer's Mountaineers (J. E. Mainer's Mountaineers). Old Time Fiddling at Union Grove. The 38th Annual Old-Time Fi..., Prestige 14039, LP (1964), trk# A.01
9. Mainer's Mountaineers (J. E. Mainer's Mountaineers). J. E. Mainer & the Mountaineers. Vol 20. 20 Old-Time Favorites, Rural Rhythm RC-250, Cas (1988), trk# B.09
10. Mainer's Mountaineers (J. E. Mainer's Mountaineers). Sounds of the South, Atlantic 7-82496-2, CD( (1993), trk# 4.01 [1959/07ca]
11. Marks, Phyllis. Folksongs and Ballads, Vol 2. Phyllis Marks, Augusta Heritage AHR 008, Cas (1991), trk# 2.11 (Thompson's Mule)
12. Pegram, George. George Pegram, Rounder 0001, LP (1970), trk# 11
13. Pegram, George; and Parham, Red (Walter). Pickin' and Blowin', Riverside RLP 12-650, LP (1959), trk# 15 [1957]
Tate, Tater (Clarence). Tater Tate, Rimrock SLP 3000, LP (196?), trk# B.01