There are four Button Man trades - starting with volume 1, The Killing Game. One of 2000ad's finest ever series, in my opinion - book four was pretty weak, though.
I would say avoid Robo-Hunter - it's very much a lighter, more comedic type of strip and is very dated. I recently bought the first Droid Files volume and to be honest I never got round to finishing it because I found it quite a chore to read.
As you said you're into Sci-fi/Cyberpunk stuff, I'd recommend; Kingdom: The Promised Land, Shakara: The Assassin, Mega-City Undercover Volume 1, B.A.D. Company: Goodbye Krool World, The Ballad of Halo Jones, Nikolai Dante: The Romanov Dynasty and some of the more recent Judge Dredd volumes like Mandroid, The Pit, Tour of Duty and Total War as these have a heavier, grittier more sci-fi feel than the earlier stuff you've been reading in the Case Files.