Old lawn mower blade, use a cut off wheel to shape it like you want it can be flattened and shaped to a certain extent with a mallet as well, cut your self a handle shape on one end and dip it in plasticoat till it builds up a decent handle
Grind an edge on it with a grinder or grinding wheel and finish with a whet stone if you want.
made one in my youth...used a leaf off a old car spring. used a grinder to shape and sharpen, went full tang with the construction, and shaped the handle from scrub-oak off an old wooden skid...... a few bolts with countersunk heads from a local hardware store, and i was all set...made a sheath from an oversize US Army garrison belt....lasted me until I got drafted when my brother lost it on a camping trip.
Flatten a tin can, split the head of a piece of short timber and insert the flattened tin at right angles to the shaft then tie tight with cord.. You could either beat it for an edge or grind it down on concrete if you don't have a file... Only be good for a few hits before the tin bent but you could reinforce it.
Use a lawnmower blade, inset in wood or just ductape it on one end. (Sharpen on stone)
Go to the local hospital, and ask to be committed. They'll give you one
Lawn mower blades are excellent.