For those of you still lacking a Bendak duel, I backtracked from the tar02_duelorg021.dlg dialog to find that the k_ptar_duel06b.ncs script contains the counter variable that determines when the duel becomes available.
I have no idea why the duel never becomes available in the K1R, because my programming methodology is rather akin to a monkey poking at a termite mound with a stick, but if you edit the numeric variable "DUEL_TIMER" from 0 to 1 in your save, then the next time you talk to Ajuur the duel can happen.
See the attached visual aid for how to easily fix it with KSE. As for fixing the actual game scripting, or how to fix it if this still fails in your specific case, you'd be better off asking a Magic 8-Ball or maybe a voodoo priestess. I consider it a miracle I figured out how to fix it for myself.
