When I was buckskinnin' I made several throwing knives, and 2 or 3 tomahawks. For the knives I have used torsion plates from old classic VW bugs, but the best ones were from chainsaw bars*, with leather scales. (*free from chainsaw repair shops.)
The "hawks" were garage sale hatchets shape-shifted with an angle grinder. New handles were made straight from hammer & axe handles.
The length of both hawk & knife should be the same, and the length measured from elbow to knuckles of a closed fist. That came to 16 inches for me. That way they make close to identical "turns", on the way to the target. After a lot of practice you can stick at most ranges, by altering the speed and follow-thru of the throw. I practiced a lot (Thereby being accused of taking an unfair advantage!) and could stick about 50% of throws up to 10 paces (3 full turns) and the "thunk" was very satisfying. The best hawk & knife man I knew had been a Logging skills competitor who could stick a double-bitted axe at 25 yards;- for money! A good score on the knife and hawk trail in our local competitions could usually lead to a top combined score for the overall prize.