Well interesting story, i'm 17 at the moment and i've been a part time architect for 1 year now and while i was designing a house i thought i'll design a weapon. But of course at that specific time i was watching Naruto and thought I'll make a Kunai.I did some research how to make them this is the site
Secrets of Shuriken-do, the Japanese art of blade throwing homepage
If you want specific details how to make them I'll do that for you but its hard work.