UPDATE! 1. It looks like Drew++ is working on a PBR shader in the Tech Artists WAYWO thread. 2. I also found a solution that is pretty damn sweet. I had never heard of Octane Render, but it's a GPU renderer that is near real-time and uses PBR http://render.otoy.com/ Check it out!
I am not sure there are any freely available. I wish there were some nice PBR viewport shaders for max. Meanwhile, wouldn't the built-in mental ray and it's custom shaders suffice if you are just looking for some portfolio renders? I know it's not real-time, but the Realtime and Offline rendering worlds have been…