Unless you set it up with them before hand, I doubt there is a way to get one on site. I guess the worst case would be that your companion car just parks in general camping. I don't know how you contacted musictoday, but calling them seems to provide much better results than email.
If the car arriving Friday is your companion vehicle, you won't be able to park there even if you had the companion pass. The companion vehicle has to go in with the RV at the same time to be able to park with it. I would imagine you could drive up and unload your stuff at the RV though. The problem you would probably run into with the companion vehicle arriving Friday is that there may be no room place to park it, since all the other RVs around you are already set up.