Good question. I recently got the game myself, and it took me a little over a year. Its a bit tricky to get. Look on E-bay, Amazon, Gamestop, Dimple, and Craigslist. If buying off of craigslist,...
At http://www.amazon.com/Star-Fox-Assault-GameCube/dp/B0002ILS24/ref=sr_1_1?ie=UTF8&s=videogames&qid=1306954121&sr=8-1
you have to beat all 10 missions on any difficulty without anybody retiring
Well, you beat a level on silver rank.
it's a jetpack