I actually understand where the OP is coming from.
If you go into a high rise office building they generally have a fairly large bank of elevators, they are usually fairly high speed, and they often designate certain elevators to go to certain floors only, in order to avoid the congestion of every elevator stopping at every floor. Colleges and universities generally do NOT have that same type of elevators, they are usually slower, and there are no designations for certain floors. Its not at all uncommon to have an elevator stop at the floor you are on and not be able to get on it because its full. When the elevator is your only choice, its can be a matter of extreme frustration.
Nevertheless, there is really nothing that can be done. A building has to be designed for a certain number of elevators, its not possible to add more. Buildings also have to be designed for a certain type of elevator, and its rarely possible to change that type. I also doubt that the building has sufficient elevators that they could designate one for the use of disabled students only.
What the OP CAN do is request accomodation for being unable to control when he can get on an elevator and get to class...in other words, get permission to be late for class, including for exams etc. He can certainly plan to arrive at school early enough to guarantee that he will get to his first class on time, its getting to class on time between classes that is his problem.
I was in his shoes...when I was working on my masters I was on crutches for part of the time (sprained ankle). It was an exercise in fairly extreme frustration.