There's a parts list in
this post.
Every rebuild will vary depending on damage, but if you're just having trouble shifting, it'll be a straight-forward job. I doubt you'll need to buy actual gears, unless you've been grinding into 3rd for years and some floating teeth got munched between them.
And regarding shifting "as fast as I want from first to second", I've never heard of any 915 that is quick in that transition.
