wonder if you could use a large dia disc blade.
some of them are in the 22-26" range.
just lay the old blade over the new one, center it and with your torch, blow out the attachment holes.
have never priced one of those large disc blades, they may be just as high as the correct part, if you can find it.
I bought a new plow coulter blade 18" and used this method to blow out the holes for the replacement rear guide wheel on my fergy disc plow (MF 64 bent tube disc plow).
have read that ferguson included tools inside the tube, take end cap off, I have never tried to take a end cap off, anyone know if this is true?