I would like some good track add ons like speed boosters or whatever they are called. I would also like catwalks, how do you get them?

You download them from a site. I think Vodhin is back up. You should check there.
What do you mean by speed boosters?
I recomend ATH catwalk set.

I would like some good track add ons like speed boosters or whatever they are called. I would also like catwalks, how do you get them?

By speed bosters do you mean LIMs, Magnetic Launch, or Friction Tires.

I've never heard of any speed booster downloads. There are add-ons to boost the appeal of coasters, but that's all. None of them actually affect the movement of the coaster.