Capitol Kids a childrens clothing, toys, and books store in Madison, Wisconsin, offer a spacious nursing area with changing table, sink, 2 low benches along the walls, 2 electrical outlets. Only drawback is that it's a part of the bathroom and not separate, but considering it's not a large retail store, it's great they considered the needs of nursing others shopping or passing through.
You Can request a chair. Non shoppers welcome. Best to call ahead.