1994 BMW 325ic convertible top wont go down

I just bought this car a few months ago and of course the top will no longer go down. I could tell that the motor was getting weak because it kept slowing down. I understand that there is an electrical motor that needs to be replaced but I CAN'T FIND THE PARTS ANYWHERE! If anyone could please direct me as to where to find the motor to replace it I would greatly appreciate it. I believe I can install in myself but I am going to get the 3 series companion book by berkly. Thank you very much to any who see this and can help. ~Reed Waters SD, CA