I have some of the earliest issues where Death's Head II (a.k.a. Minion) appears:
I imagine that, being the earliest issues, they would contain the most information about the origins of Minion, but in reading through them I found no mention of where his original organic components came from.
Minion's bio from Marvel Universe contains this story synopsis:
Death's Head returned to 2020 A.D., seeking to discover whom Necker had killed to procure his organic components. The Light Brigade, dedicated to preventing paradox, stopped him from interfering in his own creation, and sent him back to Earth-616, to seek answers from Necker in that time zone. Though briefly diverted from his mission twice to fight alongside Killpower and other Earth heroes against the demonic gestalt known as the Battletide, Death's Head finally located Necker's mother, Stealth of the armored mercenary Requiem Sharks, whom he convinced to assist him. They found Necker having ensconced herself in present-day A.I.M., working on yet another Minion cyborg; unfortunately, the human component of this Minion proved to be the past half of the time-split Charnel, who used A.I.M. technology to reunite his scattered parts and threaten the world anew. Working together, Necker, the Sharks, Tuck and Death's Head just barely destroyed Charnel before he grew too powerful to stop.
So, it appears that the search for the source of his organic components was part of a storyline (Death's Head II, Volume 2, issues #10-12), but it doesn't appear to have ever been resolved before the comic ended its run.
For what it's worth, Minion's predecessor Death Wreck had its organic components come from a homeless man.