You don't this was meant to be gave when you find all 13 skulls.
Yes, you can actually. There are 13 skulls in all. If you collect all of the skulls you will get hyabussa armor.
http://www.youtube.com/watch?v=XIE7I2OPgyA guide to all 13 skulls
To obtain Hayabusa Powered Assault Armor, you must collect campaign skulls in Halo 3. To get the helmet, you must obtain all 13 skulls. For the shoulders, you must obtain 9 skulls. For the chest plate, you must obtain five skulls. For skull locations, see the following article: http://halo.wikia.com/wiki/Halo_3_Skulls
find all 13 campaign skulls
Youtube
http://www.youtube.com/watch?v=XIE7I2OPgyA guide to all 13
About 13
there is 13 skulls 4 silver and 9 gold (the gold you only get the acheivments for).
you hav 2 get all the achievements even the xbox live ones
you can get all of the skulls on multiplayer. =)
Get 1000 gamerscore for specifically Halo 3. You also unlock the Security Helmet.