Hitman Volume 1

Demon Annual 2
Batman Chronicles 4 (“Hitman”)
Hitman 1–3 (“A Rage in Arkham”)
Hitman 4–7 (“Ten Thousand Bullets”)
Hitman 8 (“The Night the Lights Went Out”)
Hitman 9–12 (“Local Hero”)
Hitman 13–14 (“Zombie Night at the Gotham Aquarium”)
Hitman Annual 1
Hitman 15–20 (“Ace of Killers”)
Azrael 35 (“The Angel & The Hitman”)

Hitman Volume 2

Hitman 21 (“Kiss Me”)
Hitman 22 (“The Santa Contract”)
Resurrection Man 9–10
Hitman 23–28 (“Who Dares Wins”)
Hitman 29–33 (“Tommy’s Heroes”)
Hitman 1,000,000
Hitman 34 (“Of Thee I Sing”)
Superman 80-Page Giant 1 (“How To Be A Super-Hero!”)
Hitman 35–36 (“Katie”)
Hitman 37–38 (“Dead Man’s Land”)

Hitman Volume 3

Hitman 39–43 (“For Tomorrow”)
Hitman 44–46 (“Fresh Meat”)
Hitman 47–50 (“The Old Dog”)
Hitman/Lobo: That Stupid Bastich
Hitman 51–52 (“Super Guy”)
Hitman 53–60 (“Closing Time”)
JLA/Hitman 1–2

If you don’t want to include the Azrael or Resurrection Man issues, that’s fine, they’re not essential. These volumes aren’t bursting at the seams, though, and Tommy didn’t exactly have much facetime outside of his own series. Your call.