Tom, Sorry to say I believe that motor mount has been out of production for a very long time, so unless you found someone with old parts in the back room, or an old boat that maybe someone parted out, that's unfortunately the bad news. I've only actually seen one of those type of outboard mounts once, and that was on the first Potter-18 made by International Marine back in the early 70's. Why not just replace it with a new style motor mount? Fairly easy to find on Craigslist and eBay, and they will be much easier to use.
Don