The latest CG is in scene WGFMG004B "Soba Shop Showdown". You can access it using the debug menu, just make sure you set it to size 5 if that's not where your save file is currently at.
This scene and the one before it are normally unlocked by the reader having completed WGFMG001 and has advanced past scene 074 but not passed 079.
Hope that helps. Unfortunately we don't have a way to make the new CGs unlock retroactively if he player has already viewed the scene prior to the CG being added to the game. It has to be accessed in game to be added to the gallery.