Yes they are...
....euro rear bumper blocks. Stock on euro 73-78 x1/9s.
They are available seperately from the bumper blades.
Go to Ebay germany - in the search window type in "Fiat X1/9 bumper" and they will come right up. If I was smarter I would post a link! I'm sure someone else out there can do this.
He may have trimmed them a little - hard to tell from the photo. The rear bumper block is the one second from the left in the Ebay photo.
They are also available from places in Italy and elsewhere in Europe. Some will sell you only fronts or rears. A little cheaper than the German vendor. Let me know and I can lead you to them.
As you can see from the Ebay photo, they should be easy to bolt to a custom bracket.
Hope this helps. Cheers, Doug