Could always try a different dealer, its possible that another “group” may have one in stock so worth ringing a few just in case.
Pretty sure that you can have the servicing done by any Motability dealer and not just the supplying one, so no worries with looking / ordering from further afield for one and using somewhere local for everything else.
There is also a small possibility that a dealer will have a cancelled ordered, may have some extra (chargeable) options but some forum members have gotten good deals that way as unless the car is in high demand the dealer doesn’t want to have an unsold but paid for them car sitting around too long.