Great question sir!
1. Harry Greb, I say this emphatically as nobody in the annals of boxing history threw and landed as many punches rouind after round as did 'The Pittsburgh Windmill" Harry Greb! It's been said that you didn't fight Greb, you fought to keep him off you and that fighting him was like having a thouwand boxing gloves raining on you. And he was tireless and wold increase the volume of punches thrown at his opponent as the fight wore on. I have no doubt about Greb andI don't care about the lack of film footage either. Threw punches from nearly impossible angles.
2. Henry Armstrong. "Homicide Hank" is considered f the greatest fighters of all time and one of the reasons is because of his aggressive way of fighting. He didn't seem to be bothered by getting hit himself as long as he could get his shots in beating many of the best along the way. He was nearly a nonstop punching machine and a hard hitting one at that.
3. Aaron Pryor, The Hawk was a fearless fighter and never seemed to get tired of throwing punches. What you saw in his fights was a lot of action with his opponents usually covering up at the nearly nonstop assault. He was very aggressive and like Greb would throw punches from nearly impossible angles and like Armstrong with bad intentions.
4. Ad Wolgast. This old timer was extremely aggressive and nearly impossible to hurt as well not caring at all about defense though he paid a terrible price for it later in his life. The Michigan Wildcat engaged in many bloody brawls during his Hall o Fame career,
5. Pancho Villa. Another smaller fighter that always came to fight beating the great Jimmy Wilde along the way during his great Hall of Fame career. He was never knocked out and would always come forward raining punches on his opponents at a very fast rate.
6. Khaosai Galaxy. This great fighter who finished with a career record of 50-1-0 with 44 kayo's always moved forward during his fights relentlessly and punished his opponents with brutal body shots. The guy was really a scary fighter to face.
7. Pascual Perez. One of the greatest flyweight Champs in boxing history though he only stood about 5' tall if that. He made up with it by pure aggression from the first round to the last or until he had completely worn down his opponent.
8. Stanley Ketchel. The Michigan Assassin was a deadly brutal natural fighter and one of the greatest middleweights in boxing history. He had that loo of a fighter and really did love to fight either in the ring or as a hobo rding the boxcars or in saloons.
9. Jake LaMotta. The Bronx Bull was known for that chin of his and for being the first man to defeat the great Sugar Ray Robinson. But he was also a very aggressive fighter though not a knockout artist and worked his opponents body relentlessly and of course he was nearly impossible to hurt.
10. Joe Calzaghe. Joe finished his career undefeated at 46-0 and beat some quality fighters in the process like Bernard Hopkins. The reason for his success was his ability to throw and land lightining fast punches round after round often dazzling his opponents with that great speed of his.
Henry Armstrong
Jake Lammotta
Aaron Pryor
Julio Cesar Chavez Sr
Ike Ibeabuchi
Antonio Margarito
Roman Gonzalez
Juan Diaz
Kassim Ouma
Leo Santa Cruz and Diego Corrales
I chose those fighters cause from your question u said "non-stop". Some fighters who are known for their volume sometime change their style according to their opponent. for example Pacqaio, Calzaghe, Adamek and Holyfield throw a huge volume of punches when their opponent is flat but adjust their style against mobile boxers.
Where fighters I Mentioned in my top 10 never stop throwing, for example if Aaron Pryor or Roman Gonzalez fight a mobile fighter, they tack them down and throw "nonstop" punches rather than change their style. Which doesn't mean that their better than others, they just fit your description more.
Here they are, measured by CompuBox stats of the most thrown punches in a fight, the speed of their punches and their stamina:
1. Muhammad Ali(good examples: vs George Chuvalo I and vs Frazier III)
2. Harry Greb(only what I've heard about him, no proof)
3. Sugar Ray Robinson
4. Joe Calzaghe
5. Antonio Margarito
6. Manny Pacquaio
7. Henry Armstrong
8. Floyd Mayweather Jr.
9. Ike Ibeabuchi
10. Rocky Marciano
There are some good answers. I have to go with Henry Armstrong as #1 choice. Also Beau Jack and Aaron Pryor. Julio Cesar Chavez. Those are top ones come to my mind.
Muhammad Ali and Sugar Ray Leonard
