SWatkins:
It is great to watch your youtube of the planer taking a cut. The tool you were using looked like a smaller version of the "swan necked" tool. Many years ago, the swan necked tools were forged from much larger high carbon tool steel bar stock. No tool holders were used. The tool in your youtube is obviously a lot smaller.
The answer as to where to get another tool like the one that broke was stated by gbent. In the days when planers were in common use, most machine shops had a forge and anvil and maybe a power hammer to forge tools and hold-down hardware. Machinists were taught to forge and temper high carbon steel cutting tools when they were apprentices. In later years, shops often kept a gas fired forge around for this sort of work instead of the coal fired forge hearths.
Getting hold of some steel to make another cutting tool is going to be difficult in today's world. Finding W-1 (water hardening) bar stock, aside from John Oder's kind offer, is not so easy nowadays. If you have access to at least an anvil and a rosebud (and don't mind using a LOT of oxygen and acetylene), you can forge a new tool.
My own suggestion is to get a scrapped cutting edge from a road grader or highway snow plow truck. Those cutting edges are usually something like a 1060 steel. That steel will "take hardness" but not be up to the job that the high carbon tool steel is. What I'd do is "combine the best of both worlds": forge the shank and "swan neck" out of the 1060 steel, and if you want to play around with it, you can go so far as to harden (oil quench) and temper to maybe a brown color or on the edge of a blue color. This will leave some hardness and allow the tool shank to spring. I'd forge the business end of the tool out to a flat-topped section, and file it off nice and flat. I'd then braze a cemented carbide insert to that portion of the tool. I've got a box of rather large plain carbide inserts, probably from some large face mill cutter. They are square, about 5/8" or 3/4" on a side x maybe 1/8" thick. I got them in a load of other tooling, and while I do not own the cutter that would take them, let alone a mill big enough to run it, I do use those inserts by brazing them onto my own shanks. With a diamond wheel, I then dress the carbide to what I need.
This approach would give you a cemented carbide tool, could be ground to a broad-nose, and you'd have your swan-neck for some spring in the tool shank. Put the tool shank/swan neck in a can of damp sand to try to limit the spread of heat from the brazing so as not to draw the temper in the swan neck.
Years ago, the blacksmiths who forged cutting tools did forge weld high carbon tool steel for cutting edges to mild or medium carbon steel shanks or tool-bodies.
I would not try welding the swan necked tool that you had.