That looks like someone took a 12 point box end and cut it, rewelded it at a 90 degree angle and then ground down the sides to be flat. Wouldn't be hard to make if you can weld and grind!
What Nick said....
I am a former tool dealer, and I love to browse the catalogs of all the manufacturers.... I have never seen one that looks like that out of the box.
And, FYI, you would probably need to have a spare case laying around so you could actually measure, and form the wrench. Trying to do it in the car, engine assembled seems like a good way to waste a number of hours, and still not get it quite right.
