The Korean kid who wanted to look an American soldier until Margaret told him he was better looking than they were at his age.
The Korean farmer the gang sent to live with Radar when they found out he wasn’t as successful as he claimed.
The North Korean spy who was working as Charles’ servant and gave them a local cure for a rash the patients were suffering from.
Which one? 
Colonel “Buzz” Brighton, played by Leslie Nielson (the ‘ring banger’)
Master Sgt. Tarola in Seoul who won’t release Hawkeye’s ribs unless he gets some himself. AND with cole slaw.
“What, you sent all the way to Chicago for ribs and didn’t get any cole slaw?”
“Forgive us. We’re draftees.”
The old Korean cavalryman who stole Potter’s horse. I think his name was Mr. Pak?
And the North Korean Surgeon, Dr. Lin Tam, who was involved in the patient exchange behind enemy lines. He studied medicine at the University of Illinois with Henry.
the 100th character, in my mind should be the war itself.
So the Official 100 are
(Corporal)Sargeant Maxwell Q. Klinger
Aggie O’Shea, the reporter
B.J. “Beej” Hunnicut
Benjamin Franklin “Hawkeye” Pierce
Billy Tyler
Brandy Doyle (Gwen Verdon)
Capt. Roy Dupree (Arkansas ‘43–“Souwee hog!”)
Capt. Steven Newsome
Captain Casey (the fake doctor)
Captain Jonathan R. Tuttle
Captain Sam Pak
Captain Simmons
Carlye Walton
Charlie Lee
Col. Hollister
Colonel Daniel Webster Tucker “A shot and a beer”
Colonel Sam Flagg
Colonel Sherman Tecumseh Potter
Corporal Calvin Spaulding (played by Loudon Wainwright III)
Corporal Igor Straminsky
Corporal Walter “Radar” O’Reilly
Digger Detweiler
Donna, aka Mrs Chuck Winchester
Double Dear John John from Reno, AKA Cowboy
Dr. Borelli
Dr Tim Lam
Duke Forrest
Edwina “Nurse Eddie” Ferguson
Erin Hunnicut
Five O’Clock Charlie
Fr. Francis J Mulcahy
Gen. Wilson Spaulding Barker
General Clayton
General Douglas MacArthur (tho not a speaking role)
General Hammond
General Steele “Hey, hey, Uncle Bud, gonna beat my feet in the Mississippi mud!”
Ho-Jon
Honoria Winchester
Inga
Interviewer (Clete Roberts)
Jesus Christ (Well, he wasn’t REALLY Jesus Christ. He just thought he was.)
Kim Luck
Leo Bardonaro (James Cromwell)
Lieutenant General Robert “Iron Guts” Kelly
Lillian Rayburn
Lt Col Donald Penobscot
Lt Col Henry Blake
Lt Maggie Dish
Lt Mendenhall
Lt. Nugent
Lyle Wesson (Alex Karras)
Maj. Charles Emerson Winchester III
Maj. Frankenheimer (the officer in charge of the “Korean Theater”)
Major Frank Burns
Major Murdock
Major Sidney Theodore Friedman
Margaret “Hot Lips” (O’)Houlihan (she was more Irish in the movie)
Marine Sgt. Marty “The Trenton Tornado” Urbancik
Martine LeClerc
Mildred Potter
Mr Kwan
Nancy Sue Parker
Nurse (Lt) Baker
Nurse Bigelow
Nurse Able
Nurse Kelley
Nurse Margie Cuttler
Nurse Meg Cratty
Oliver Harmon “Spearchucker” Jones
Painless Woldowski
Peg Hunnicut
Private George Weston
Pvt Charles Lamb
Pvt. Gary Sturgis (Patrick Swayze).
Pvt. La Roche
Radar’s bunny
Radar’s teddy bear
Rosie
Seargent Zelmo Zale
Sgt. Ames
Sgt. Jerry Scully
Sister Theresa
Smilin’ Jack Mitchell
Soldier (from Point of View)
Soon-Lee (Hahn) Klinger
Sophie
Sparky, friend of company clerks everywhere
Staff Sgt. Luther Rizzo
The fellow who died holding Nurse Kellye’s hand and talking about his peachtree orchard.
The Korean Family from Hawkeye’s Jeep accident
the orphans - colletively, they count as one character
The P.A. system
The Sniper
The stuttering soldier.
The Turkish soldier with the huge moustache
Tommy Gillis
Trapper John McIntyre
Ugly John, the gas-passer
Wendell Peterson (Ron Howard)
Feel free to continue naming characters ad infinitum
I meant to answer the comment about the North Korean doctor who studied in Chicago. Someone else mention Henry went there - the NK never said he knew Henry
(oops - somehow the 100th wasn’t on there - now it is)
(Corporal)Sargeant Maxwell Q. Klinger
Aggie O’Shea, the reporter
B.J. “Beej” Hunnicut
Benjamin Franklin “Hawkeye” Pierce
Billy Tyler
Brandy Doyle (Gwen Verdon)
Capt. Roy Dupree (Arkansas ‘43–“Souwee hog!”)
Capt. Steven Newsome
Captain Casey (the fake doctor)
Captain Jonathan R. Tuttle
Captain Sam Pak
Captain Simmons
Carlye Walton
Charlie Lee
Col. Hollister
Colonel Daniel Webster Tucker “A shot and a beer”
Colonel Sam Flagg
Colonel Sherman Tecumseh Potter
Corporal Calvin Spaulding (played by Loudon Wainwright III)
Corporal Igor Straminsky
Corporal Walter “Radar” O’Reilly
Digger Detweiler
Donna, aka Mrs Chuck Winchester
Double Dear John John from Reno, AKA Cowboy
Dr. Borelli
Dr Tim Lam
Duke Forrest
Edwina “Nurse Eddie” Ferguson
Erin Hunnicut
Five O’Clock Charlie
Fr. Francis J Mulcahy
Gen. Wilson Spaulding Barker
General Clayton
General Douglas MacArthur (tho not a speaking role)
General Hammond
General Steele “Hey, hey, Uncle Bud, gonna beat my feet in the Mississippi mud!”
Ho-Jon
Honoria Winchester
Inga
Interviewer (Clete Roberts)
Jesus Christ (Well, he wasn’t REALLY Jesus Christ. He just thought he was.)
Kim Luck
Leo Bardonaro (James Cromwell)
Lieutenant General Robert “Iron Guts” Kelly
Lillian Rayburn
Lt Col Donald Penobscot
Lt Col Henry Blake
Lt Maggie Dish
Lt Mendenhall
Lt. Nugent
Lyle Wesson (Alex Karras)
Maj. Charles Emerson Winchester III
Maj. Frankenheimer (the officer in charge of the “Korean Theater”)
Major Frank Burns
Major Murdock
Major Sidney Theodore Friedman
Margaret “Hot Lips” (O’)Houlihan (she was more Irish in the movie)
Marine Sgt. Marty “The Trenton Tornado” Urbancik
Martine LeClerc
Mildred Potter
Mr Kwan
Nancy Sue Parker
Nurse (Lt) Baker
Nurse Bigelow
Nurse Able
Nurse Kelley
Nurse Margie Cuttler
Nurse Meg Cratty
Oliver Harmon “Spearchucker” Jones
Painless Woldowski
Peg Hunnicut
Private George Weston
Pvt Charles Lamb
Pvt. Gary Sturgis (Patrick Swayze).
Pvt. La Roche
Radar’s bunny
Radar’s teddy bear
Rosie
Seargent Zelmo Zale
Sgt. Ames
Sgt. Jerry Scully
Sister Theresa
Smilin’ Jack Mitchell
Soldier (from Point of View)
Soon-Lee (Hahn) Klinger
Sophie
Sparky, friend of company clerks everywhere
Staff Sgt. Luther Rizzo
The fellow who died holding Nurse Kellye’s hand and talking about his peachtree orchard.
The Korean Family from Hawkeye’s Jeep accident
the orphans - colletively, they count as one character
The P.A. system
The Sniper
The stuttering soldier.
The Turkish soldier with the huge moustache
The War, itself
Tommy Gillis
Trapper John McIntyre
Ugly John, the gas-passer
Wendell Peterson (Ron Howard)