There used to be plenty of mechanical keyboards with this layout. Now none. And I think that's a shame.
Consider, for a moment, an idealized version of the layout: build buttons into the trackball surround (the way trackball mouse buttons are often implemented) that handle the arrow key functions, and then build mouse buttons for the trackball into the bottom of the case. Actually, there was a Focus keyboard that was almost exactly like this, but it implemented the mouse buttons in a weird way, where they were small and offset to the side, whereas I'm imagining them larger, like the EnduraPro's mouse buttons, and directly under the trackball. Now with this layout:
-You could use the number pad with your right hand (your dominant hand, and how the number pad is meant to be used) while your left hand, in just one position, has access to the arrow keys, navigation cluster, and mouse (via trackball) simultaneously. Good for spreadsheets and similar work.
-When typing, the trackball could be used with the right hand, and would much closer than a conventional mouse (for a full-size keyboard), and you once again benefit from simultaneous access to mouse and arrow/navigation keys.
Here's the keyboard that is
almost right, configuration-wise...it just needs the mouse buttons moved under the trackball.

Abstracted version:
