I could certainly ship you the measurements of the buckle, but you'll have to ask the seller about the bar. (I can't imagine it will be much, though.)
There is a fellow in the UK who makes a "clone" device that performs the same function as the Porsche bar:
Porsche Airbag de Activator Alternative to Bar and Child Seat Boxster 911 | eBay
This device does not require a buckle, so it will work with any seat as it is.
Keep in mind that your Porsche dealer will have to reprogram the car to recognize the bar or switch gizmo. Best call them and make certain that they can/will do that before investing in it.