Honestly, I’m not sure any exist. Paranoia has a new edition. Ghostbusters was so rules-light and is easy to do with Fate Accelerated, anything else would needlessly complicate it. Top Secret has a new edition forthcoming. Star Frontiers is freely and legally available online and the old system works well enough for my taste. Old editions of D&D are either available in scanned form from D&D Classics or Retro-Clone form from various publishers (plus many of the core books were printed in such vast quantities they’re readily available from second-hand retailers). Metamorphosis Alpha has been reprinted. In fact, with digital scanning technology and PDF distribution, I can only think of one “dead game” I would play or run that isn’t available fairly easily: Buck Rogers XXVc. As I currently own a copy, I can run it anytime I like. If I didn’t own a copy, Rocket Age does a damn good job of capturing the same feel; creating a Buck Rogers conversion would be fairly trivial.
By and large, I’m not convinced every game needs to be updated with modern rules. Some games run just fine the way they are. I have never enjoyed a modern version of Paranoia as much as 2nd edition, for example. The rules are already simple, so a lot of changes feel, to me, like they’re change for the sake of change and they over-complicate something that just doesn’t need those rules (the players aren’t technically allowed to know the rules anyway, so what’s the point?). If it ain’t broke, don’t fix it.