appearance.2da isn't what you're looking for, only the PMBE06, PFBE06 and ia_class6_006 files determine an Exar Kun reskin. They end in ".tga" so "PMBE06.tga"
Have you tried K1R? I vaguely remember seeing those files in that mod years ago. If it's not in K1R, and you can't find it in either the NPC Overhaul or Shem's mod, as SH has said already we can't be of much help without images of the armor in question.