I wonder if you contact Motability and explain they may be able to give you a list of cars suitable for the insurance cap for under 25’s
Dare I say it could be an advance search feature on the Motability site to enable under 25’s to see all the cars available to them.
I am not sure if you have had a Motability car before but the ordering and delivery time will vary depending on whether you go for a stock car (usually a lot quicker) or a new build (which can take 6 months and upwards to 9 months, you do get the exact specification you want.
If you are more flexible then it worth negotiating a deal as they are there to be had if you ask with a smile what can they discount either Ap or optional extras some times you get upgraded premium car mats free tank of Gas it all depends on you and the salesperson on the day so do your research and ring up different branches and get some information..
if you are going for a stock car I would advise on making a deal quickly as the car could disappear at any time as someone else might be after it too
Good luck