Honestly, I don't even know what to help you with. I've heard of companies that do this, but there are so many that I can't give you any specific advice.
I agree with the previous post, because among the large number of bus rental companies in Berlin, it is wise to choose one that has enough experience and also knows the country and its capital. I myself had a problem finding such a company, but I managed to find a bus hire berlin company in which I was able to rent the bus I needed. I think this service is exactly what you need.
