Ko katana sized ring pommel miao dao

What might a ko-katana sized miao dao be? That's like asking for a gladius sized longsword.

The cheap solution is to convert a ko katana into a miao dao (or get somebody to do it for you). Adding a ring pommel to a katana tang is easy enough (I'd call it easy enough to DIY, but YMMV.) Reshape the tip if you want a miao dao profile. Done!

Conversion rather than custom-from-scratch increases your options.

To add a ring pommel: Get a ring, remove tsuka, grind end of tang to fit ring, weld ring to tang, put steel strap over ring and tang, weld to ring and end of tang, weld and/or rivet strap to tang, unwrap tsuka, split tsuka core, reshape pommel end of tsuka to fit pommel end of tang, put tsuka core back together on tang, pin and wrap.

Or weld ring to strap only, and pin to tang, and you have a removable ring pommel, which you might like if you ever want to change the tsuba.

(You could also convert a cutlass or hanger blade - some of the Windlass blades look OK. This gives you a more miao dao blade, but I think the conversion would be more work.)

You don't need to be able to weld. It's easier to find somebody who can weld than somebody who can make a sword blade.

There are non-welded solutions, too. If you use a large flat washer (or a couple of them, stacked) for the ring, you should be able to use a strap riveted to both ring and tang. Maybe cut a washer-plus-tongue out of sheet, put one on each side of the washer, and rivet the tongues to the tang. You could bolt rather than rivet, and have it easily removable. Lots of options!

(Of course, you don't have to do riveted/bolted solutions yourself, either. It's easier to find somebody who can drill though a tang and rivet/bolt than somebody who can make a sword blade.)