you need to have one custom made, all steel, not wood. Leaf springs off a truck can be made into very good spear blades. get you some 1/4 inch pipe, threaded in 2 - 4ft sections and have you a hilt on the back of it for a stabbing spear.
Find a custom knife maker or a blacksmith in your area that can help you.
For a throwing spear you'll need to also have one made to your own specifications, that way you are comfortable with it and know the particular weapon as opposed to one you ordered out of a catalog.