The battery chargers and battery pack wiring harness are both listed on the new GT 450 parts page.
The speed controller will usually last for as long as it has not been overheated. If it is used gently and not allowed to overheat then it should last as long as the scooter does. However if it is overheated from the scooter being driven up a hill that is too steep for it or from another event that causes it to overheat then it could burn out and need to be replaced.
Please let us know if you have any questions.