Its highly unlikely Motability will help, as technically you aren’t a customer yet.
What VW model have your ordered? Its worth remembering VW is a huge group and other brands in that group will have basically the same car, that may be available from stock within 5 days as Rhodgie has said. Equally, it might be worth you expanding your search outside the VW group to!
Look on Autotrader, for new cars available from stock in your area or further a field if you can get there. If there is something you like, ring them up and ask if they are willing to let you have it, as a Motability car.