Zoom (partially lost revival of PBS children's series; 1999-2005)
The 1999 revival of the series ZOOM was never released on Home Media, bar a few special VHS tapes "The Making Of..." and "Party With..." and by the second half of 2007, had been taken off the air completely, and has not returned since.
Eventually, a number of individual segments were released onto Youtube by various users, and in 2011, about half of season 2 was as well by user ZOOMerTube.
As of the summer of 2015, all episodes from seasons 2-7 and 11 episodes of season 1 have been found, uploaded onto Youtube by user ZOOMFan1, who had gone to the lengths of recording them all twice while they were on the air. Unfortunately, by the time he started watching, season 1 would only be syndicated once more (in late 2002/early 2003), and 30 episodes that were originally a part of the season would be skipped over. Although many individual segments from them were uploaded in circa 2010 by user KrisTheKnight, the episodes in their entirety are still at large. The episodes were respectively episodes 105 through 134.
In addition to this, many segments that were filmed for the show remain unaired. Some, if not all of them, are available on the website. In addition to this, what appears to be a teaser of one appears at the end of episode 233 at the 26:52 mark.