i think what you need to do is come up with a shortlist and ring around the dealers and see what they have of each one in stock and go from there. if i hadnt wanted a particular colour or trim the local mini dealer had 3 countrymans in stock. likewise with the suzuki and seat dealers.
i would spend an afternoon ringing each dealer and explain your needs and that its motability and ask what they have in stock. some will even move stock around the country for you. so a mini dealer may find you a car in at a dealer in scotland and if you say thats the one move it down to you.