Try your local school bus company for classes. They may allow you to participate in their training for new drivers. I suspect that it will be expensive though.
You can practice in a parking lot. The main issue is the turning radius of the back wheels and the need to go far into an intersection before turning the front wheels. That and parallel parking :)
They look bigger than they are. You may need to reverse a time or two on Cul-de-Sac streets and watch out for crossings/driveways where you have a steep approach or departure angle but otherwise you will be fine.
