There have been a number of TMNT manga published in Japan which have never been released in the West.
Mutant Turtles Gaiden is a collection of short stories drawn and written by Hiroshi Kanno and published by Dengeki Comics.
|Chapter 4: Discover Japan!||August 30, 2016|
|Chapter 3: The Strongest Weapon: The Devil's Monster||August 30, 2016|
|Chapter 2: Beat the Phony Turtles||August 30, 2016|
|Chapter 1: The Ninja Turtles Drop In!||August 30, 2016|