public static Object Resources.GetBuiltinResource(Type type, string path)
I can’t find any informations about that at all.
plz, let me know about that. 
Presumably it gets Default-Diffuse, Default-Particle and the other little stand-ins.
However, since it is undocumented, you should definitely not use it. Fortunately, it’s probably not very interesting either (unlike the terraindata internals that were not documented in early Unity versions), so easy to resist.