I feel your pain, I'm on the hunt for King Krush at the moment too.
Right now I'd take finding him dead over this complete lack of anything that I've been having. Nearly ten days of regular patrols and I've not seen him dead, alive, newly tamed or anything. The same goes for the other Basin rares too. I seem to be chronically unlucky when it comes to him, I've never had this much trouble finding a rare before. Even an overnight (finally, insomnia has a benefit!!) eight hour stretch when I had the whole zone to myself yielded nothing.
At least finding his corpse would give me some kind of spawn time estimate
Edited: Would you believe I have just happened across him near the gorillas and tamed him?! Hang on in there, you'll get him!!!!