This repository contains an addon for Blender 3.x that can import Stunt GP models.
Old version of a script created by Martin for Blender 2.79 is available here: https://forum.rvgl.org/viewtopic.php?t=391
The whole addon is stored in the io_scene_pmd directory.
https://docs.blender.org/manual/en/latest/editors/preferences/addons.html