The original series could've been this very easily around November 1973 had Groucho's grandson Andy not answered the phone one day (while Groucho had Jack Nicholson, Elliott Gould, and Marcel Marceau as guests). The person on the other end, a man working at the NBC storage warehouse in Englewood Cliifs, New Jersey, was part of a group that was destroying a bunch of 1950s-60s shows to clear space for newer programs. When Groucho responded with "Tell him to burn them for all I care" (which got laughs from his guests, although Andy couldn't tell "if he was just doing his grouchy act for his invited audience or truly didn't care"), Andy reminded him how Oscar Levant's Information Please was destroyed and Nicholson convinced Groucho to accept the reels.
Two weeks later, it turned out that "several boxes" was in fact 5,000 reels in 500 boxes, consisting of not only the entire series but also the Edited for Syndication "The Best of Groucho" package. Andy and show creator John Guedel pitched the idea of airing the episodes in late nights on KTLA, which the station executive liked with one provision: someone had to go through all the shows first. That someone was Andy, who was paid $150 a week to spend eight hours a day at Groucho's house watching and archiving the episodes.
That said, some episodes (including Groucho's Grand Finale and the only color episode of the original run) haven't been seen in many years.
The Hackett version had no circulating episodes until one showed up in February 2010 — which, amazingly, is also the only time in this run that the Secret Word was said. There's also this brief clip.