For those guests using a mobility scooter, wheelchair, electric wheelchair, ECV, electronic convenience vehicle at Walt Disney World theme parks they have discontinued the Guest Assistance Card and replaced it with the Disability Access Service (DAS). The good news is mobility scooter users do not need a DAS card.  Following is an excerpt from their website:

Does a Guest whose disability is based on the necessity to use a wheelchair or scooter need a DAS Card?
No, a Guest whose disability is based on the necessity to use a wheelchair or scooter does not need a DAS Card. Depending on the attraction, the Guest will either wait in the standard queue or receive a return time at the attraction based on the current wait time.

To ensure you get the best scooter for your needs, reserve your Orlando scooter as far in advance as possible.  With a liberal cancellation policy of 48 hours before arrival, there is no reason not ensure you will have what you need, when you need it.  The scooter will be delivered to you at your hotel, resort etc. or you can arrange a meet and greet at the airport to take delivery.  Scooter Vacations has six models to choose from and all provide 12-15 hours of theme park ride time to ensure you can spend a full day at the theme parks.