The KiCad library maintains a repository for 3D source files at https://github.com/kicad/kicad-packages3d-source.
The source files used to generate 3D model data should be submitted to this repository when a user contributes 3D model data.
Source files include file generator scripts, or native model files from source software (e.g. FreeCAD).
The source repository directory structure mirrors that of the kicad-packages-3d repository.