Will these work?
http://www.equipt1.com/item/g-clamp-oem-roof-rack-awning-mounting-brackets
This supplier has some other cool stuff. I also heard Rhinorack is coming out with some new options for the 4 runner but he gave no ETA. I would call them and see what info they can give you.
I've used these before on 3rd gen 4runner and they worked great. They fit on my 4th gen and I might use them for an awning but I'm not quite sure on the strength. Would prefer the equipt1 linked above for strength concerns.
https://www.yakima.com/mighty-mount-39h