My searching indicates you're pretty right that these albums are few and far between. I only found one recording from any of their albums that you hadn't already, though I did find quite a few live recordings you may not have seen.

Just to put it all in one place:

OLD FAMILIAR TUNES - Flying Crow FC-104 - 1980 - listen
A1 Johnson Gal
A2 Davy
A3 I'm S-A-V-E-D
A4 Sweet Milk & Peaches
A5 A Lazy Farmer Boy
A6 Merry Girl
A7 George Washington
A8 Negro Suppertime
B1 Come Over & See Me Sometime
B2 Belle Of Lexington
B3 Billy Grimes / The Rover
B4 Got No Honey Babe Now
B5 Eighth Of January
B6 Give Me Back My Fifteen Cents
B7 Just Drink Some Cider
B8 Indian War Whoop

SONGS OF THE HILLS AND PLAINS - Cinnamon 1201 - 1981
A1 Georgia Fox Trot
A2 Where The Irish Potatoes Grow
A3 She's A Hard-Boiled Rose
A4 Lone Star Trail
A5 Who's Been Giving You Corn?
A6 Riley The Furniture Man
A7 Throw The Old Cow Over The Fence
B1 Give Me A Chaw Of Tobacco
B2 Dark Eyes
B3 Walls Of Jericho
B4 Old Joe
B5 Oh, Lovin' Babe
B6 Sullivan's Hollow
B7 Katy Dear
B8 Go On, Nora Lee
B9 There's No Hell In Georgia

JUST GIVE ME THE LEAVINGS - Marimac 9003 - 1985
A1 Georgia Hobo
A2 The Deacon & His Calf
A3 Acadian Blues
A4 Lone Star
A5 Jim Sapp
A6 Just Give Me The Leavings
A7 Hometown Blues
A7 Lifeline
A9 Old Folks Get in Bed
A10 Lilly Of the Valley
A11 Only A Message From Home
B1 How Long
B2 Howdy Bill
B3 Jack Leg Wobble
B4 May Dearest May
B5 Far In The Mountain
B6 Lonesome Road Blues
B7 Weavily Wheat
B8 Captain Won't You Let Me Go Home
B9 Sugar In The Gourd / Sugar Hill
B10 Chevrolet Six

JUST HILLBILLY - Global Village C 303 - 1985
A1 Old Blue Sow
A2 Diamond Joe
A3 Don't Get Trouble In You Mind
A4 Ducks In The Millpond
A5 Goodbye My Honey, I'm Gone (at about 50 minutes in ***)
A6 Jenny Baker
A7 Old Uncle Ned
B1 Yellow Rose Of Texas
B2 May, Dearest May
B3 John Goodwin
B4 Cluck Old Hen
B5 Billy In The Lowground
B6 Old Folks, Get In Bed

*** - note that this version is officially from The Young Fogies compilation album and not this album, though the recording is probably the same... the liner notes to The Young Fogies, of which I own a copy, indicate Pat Conte donated a "master tape" for the album's production.

WHEN THE YANKEES CAME DOWN - Marimac Recordings 9006 - 1986
A1 Fishing Time
A2 Somebody's Waiting For Me
A3 9 O'Clock Breakdown
A4 Jawbone
A5 I'm Going To Leave Old Arkansas
A6 I'm Saving Up Coupons
A7 When Rueben Comes To Town
A8 Hide Away
A9 Lonesome Road Blues
A10 Snowdrop
B1 Home Town Blues
B2 My Ozark Mountain Home
B3 Arcadian Waltz
B4 The Old Arm Chair
B5 Because He Loved Her So
B6 Round Town Gal
B7 How Long
B8 Green Valley Waltz
B9 Bath House Blues
B10 The Little Black Train
B11 Wimbush Rag

(source - also contains pictures)


* * * * * *


The University of North Carolina at Chapel Hill also has a few live recordings of theirs digitized. Note that the audio links below don't contain a track list, but the finding aid, linked on each page, does.

RHYTHM GORILLAS, GREENVILLE, OHIO - BRANDYWINE - home recording (SFC Audio Cassette 3680) - 1982 - side 1 / side 2
2.1 C'mon Girls Let's Go Walkin'
2.2 The Moonshine Hollow Band
2.3 Rattlesnake Dick
2.4 [Racist slur]'s Wail
2.5 Raccoon on the Rail
2.6 Cheverolet 6 [sic]
2.7 Old Folks Never Go to Bed
2.8 The Old Belle Cow
2.9 Married Life Blues
2.10 Picture on the Wall

OLD TIME BANDS WORKSHOP - KENT STATE FOLK FESTIVAL - home recording (SFC Audio Cassette 3672) - 1987 - side 1 / side 2
Side One: Canebrake Rattlers.
1.1 Greasy String
1.2 Old Jazz
1.3 Cotton Mill Blues
1.4 Sweetest Gift is a Mother's Smile
1.5 Turn Your Radio On
1.6 Far On the Mountain
1.7 Cripple Creek
1.8 Green River
1.9 Rag
Side Two: Pat Conte, Kerry Blech, Shelia Blech, Mark Farrell
2.1 Winbush Rag - Pat Conte, Kerry Blech, Shelia Blech, Mark Farrell.
2.2 Tell Her Lies Feed Her Candy - Kerry Blech, Shelia Blech.
2.3 Hump Backed Mule
2.4 Virginia Reel
2.5 Gimme Chaw of Tobacco
2.6 Old Uncle Ned

STRINGBAND WORKSHOP - KENT STATE FOLK FESTIVAL - home recording (SFC Audio Cassette 3675) - 1987 - side 1 / side 2
1.5 Richmond Cotillion
1.6 Yellow Rose of Texas
2.10 John Henry - Matokie Slaughter, Andy Cahan, Alice Gerrard, the Rattlers, the Canebrake Rattlers
2.11 9 O'Clock Breakdown
2.12 Unidentified
2.13 Whoa Mule
2.14 Talk
2.15 Johnson Boys
2.16 How Long [?]
2.17 O'er the Raging Sea [fragment]

Some final random live recordings

Tracy's Family Festival, 1983 - Lonesome Road Blues - listen
Croton Point Park(?), ca. 1988 - Say Darling Say - listen
Brandywine, 1993 - When the Roses Bloom Again - listen
Brandywine, 1993 - Goodbye My Honey I'm Gone - listen
Brandywine, undated - Hook and Line - listen

Also, read an interview with The Otis Brothers (and Pat Conte) here, pages 3-5