Found some other options
So called "Photo ball head", available at LHS, not sure about prices and materials
Image may be NSFW.
Clik here to view.
Also, you have McMaster-Carr with steel 3/4" balls..
[www.mcmaster.com]
And finally, take a look at Stud Mount Ball Transfer , like these
[www.vxb.com]
So called "Photo ball head", available at LHS, not sure about prices and materials
Image may be NSFW.
Clik here to view.

Also, you have McMaster-Carr with steel 3/4" balls..
[www.mcmaster.com]
And finally, take a look at Stud Mount Ball Transfer , like these
[www.vxb.com]