There are quite a lot of transportation companies in Germany. I don't know what your budget is, but I think bcs-bus.com will help you out. You can reserve a bus there shortly before the trip. I've used this company many times and I'm very satisfied with the service. The drivers speak good English, which was one of the deciding factors in choosing this transportation company. We had a slight change of route and time just before the trip, so we were able to negotiate all the nuances with the driver right on the spot. I recommend you to contact here, they are really professionals.