Such Marines are inside Dreadnoughts
When the greatest of the Astartes are crippled in combat the Battle-Brother's body will be repaired and transferred into an armoured cyborganic sarcophagus outfitted with extensive life support systems. This sarcophagus is then interred within the heart of the armoured body of a Dreadnought if there is even a spark of life left.
As a Dreadnought, Marine can live almost infinitely - Bjorn the Fell Handed is over 10,000 years old. Unfortunately, with age comes slowly madness, so Dreadnoughs spend most of their time asleep and they are awoken only in the time of need.
Of course, there is also the effect of the Warp - There are many Chaos Space Marines that still remember the Great Crusade and Horus Heresy: while for the material world it has been over 10,000 years, for them it was barely a few decades ago - for example, Kharn the Betrayer was with World Eaters (called back then "War Hounds") before this legion has been united with their primarch Angron, yet he is still alive.
But the premise of the question is bit faulty: saying that there are humans that can live theoretically longer than Astartes is untrue - yes, there are quite a few life-extending methods - starting from simple medical treatments, through severe mechanical augmentation to sorcery - but the Space Marines don't need them, since they can naturally have a very long lifespan. Mentioned previously Dante is over 1,500 years old. And in the "Salamanders" series, there is a lonely survivor from the Istvaan V massacre, which has taken place almost 10,000 years ago:
Gravius was the Captain of the Salamanders Legion's 5th Company, during the Great Crusade and he took part in the Conquest of One-Five-Four Four with his friend, Captain Heka'tan1. As the Horus Heresy unfolded, both Captains would take part in the war against the Traitor Legions on Isstvan V, but when the Dropsite Massacre began[2[...]In M41, Gravius was found alive by fellow Salamanders from the Chapter's 3rd Company, but the Captain was now in a horrifically withered and frail state.
Gravious was alive, yet immobile, livig through his sense of duty. In normal circumastances, aging Salamanders seek death, but it is not explained at which age Marine is considered "aging"
“I don’t know what I believe at this point,” he admitted. “The warp storms could have affected the passage
of time. But it’s also entirely possible that this Salamander is simply many years old, longevity being a
benefit of our slow metabolic rate. Such a thing has never been tested, given that most of our number
invariably meet their end in war or, if death is not forthcoming and age arrives first, by wandering out into
the Scorian Plain or setting sail on the Acerbian Sea to find peace. It is the way of the Promethean Creed.”
Last but not least are Primaris Marines - while they appeared recently in the Imperium, their history is as old as Horus Heresy, when Roboute Guilliman charged Archmagos Dominus Cawl with creating a new legion of warriors that would aid the Imperium in its next darkest hour. Cawl was working on this task up to M42 when he finally released the new breed of Marines that was kept all this time in stasis.
Also, I just found about the Helfathers - a Iron Hands honor guard that is made entirely from resurrected (and augmented to the point where they are barely alive) warriors. There is a little information about them, but it seems that many of them died more than once, turning them into sort of Imperial Necrons.