Goku Did make a spirit bomb while Super Saiya-Jin, But it was in a movie. It was put in the movie to show how pure hearted Goku is. Because in order to go Super Saiya-Jin, you need anger. But with anger you don't have a pure heart. And you need a pure heart in order to create a spirit bomb, or it will destroy you. (thats what it does, destroys all evil if powerful enough) and in the cooler movie i think, goku went ssj and created a spirit bomb. and King Kai mentioned that even as SSJ goku was pure hearted.
But it will never be put in the game because they don't do movies...