This one is obviously made by removing the bottom of a can and trimming it.
You can get metal backings at any crafts store. We don't yet sell plastic backings, so the easiest way to mount them is to flatten the back of the button a bit with a coin (hammer it a bit) and then glue-on the backing.
Or, if you've bought metal backings having holes in them, then you can rivet them in as shown in the photo above.
And, if you like these, consider the 3D photo stands you can make:.
Or consider making floating photo frames:
