Blog:Lost & Found
Two arcade games thought gone forever have resurfaced. The first was Megumi Rescue, a title developed by Aicom and Eleca in which you must put out burning buildings and rescue the people inside. The original arcade version never made it past location test, but a Mark III/Master System version that uses the paddle controller was released. The board turned up in a 2011 eBay auction and was purchased by a Japanese buyer, and a video turned up on YouTube in 2012.
Next was Planet Probe. I originally saw this one in the US copyright records and wrote a blog post about it. Things snowballed from there. A board was found, the ROMs were dumped, and it is now playable in MAME.  
There are still plenty of lost games, of course, like Shounen Majutsushi Indy (Indy the Magical Kid). This Dragon Quest-esque RPG for the Famicom was demonstrated on a Japanese TV show The TV Power but was never released. It was to be published by IGS and sounds like a Graphic Research game.
Speaking of unreleased Famicom games, here's a promotional video for Nichibutsu's Genjuu Souseiki (Genesis of the Mythical Beasts), which is more of a strategy game: