@Killer_DM Bob, see Raddu’s post here releasing all unpublished stuff from Athas.org
It has the CS of Kurn in there, and the Lost Cities of the Trembling Plains.
Both feature stuff on Kurn. Not all is finished but the history part at least is elaborated enough to be usable (what I gained from a speedy gloss over it, that is, haven’t had time to fully read those).
Relatedly there is also the Athas.org released Wisdom of the Drylanders and Faces of the Forgotten North that treat Kurnan organisation or NPCs.