To help you find a specific controller, we'll need more info.
What motor do you have?
What battery do you have?
What is your exact usage scenario? (terrain, speed, riding style, throttle, PAS, wind, hills, on road / offroad, stop start traffic, open road, range, etc)
Does it need to only run "in reverse", or does it have to be able to change directions?
Those will help us help you make sure you have the right system to do what you want.