Wrecking yards or transmission rebuild shops usually know. When trying to locate or find second hand parts, the best way post a request to many wrecking yards at the same time is to Google the words "wrecking yard parts" or "used auto parts" if you want to be a little more specific enter the manufacturer of your vehicle example "BMW used parts". May links appear that allow you to enter the details of your vehicle and the parts you are looking for. This request is then sent out to thousands of wrecking yards through out the country and they then send you an email or give you a call with the price and availability of the part. it is the wrecking yard that pays a small commission for the service.