My two cents on this would be to not limit yourself to just wood for the banister. I had surprisingly good success on a show in grad school using what my TD referred to as "coil pipe." It was some sort of stiff plastic tubing that came in a big coil. It was easily made to conform to the curve of the staircase, but was stiff enough to not deflect when people leaned on it. Nobody was sliding down it, mind you, but it worked well for that application.
With limited fabrication resources, the key is going to be finding a material that is relatively easy to work with in individual pieces but can be laminated or built up into something that's strong enough for what you want to do with it. Depending on the radius of the curve, you might be able to use plywood or narrow steel tubes or strips of one-by or any manner of long, thin material. Of course, the other route is to try to find something that already exists that you can incorporate into your set. It might be worth calling custom staircase companies in your area to see if they have something they could lend you.