If I try and load new 3D materials using the "Load Materials" menu item Photoshop sends me to a web page which no longer allows logins due to the transition to Revel. Since Revel appears to be for user content I cant see why the 3D materials would be there.
Where are the additional 3D textures for Photoshop ? I have searched Adobe.com but cant find a mention of them directly.
I just tried on a windows 7 machine with cs6 and was able to get to the web page and download the materials without signing in
by clicking on Versatile Materials using a Firefox browser.
I tried both 3d>Get More Content and Load Materials as you did.
Maybe if you go to the page without going through photoshop: