The original post was dated 2/10 of '19 so, I don't know if the OP has acquired or made one but, just in case he (or anyone) may be a bit "spendthrift" and want to make one from CHEAP. All I did was purchase a 3" long, 1 1/2" threaded, steel nipple. I already had one of the notched steering head nuts off so, all I did was sort of "trace" the notches into the tip of the nipple. Then, with my trusty hack saw, cut out what I needed to remove. And, with a bit of fineness of some small files, vuuuuuuaallllllaaaa, we have one steering head socket. Oh, almost forgot. I needed a way to use a 1/2" drive ratchet on it. So, out came my trusty Plasma cutter and I maed a square hole in a piece of metal that, I cut to the exact length to weld onto the top of the nipple. DONE!
That tool worked absolutely flawless. I realize that not all folks have trusty Plasma cutters and MIG welders laying ing around so, there's alternate ways of making this work. Brazing is one or even Silver soldering since Silver soldering is fairly strong, at least strong enough for the torque needed on these nuts. Anyway, take a look and see if it's something either the OP or anyone might be interested in making. I think it took me a whopping 1 hour to make.