Private attorneys shall be appointed in a substantial proportion of the cases. Each plan may include, in addition to the provisions for private attorneys, either of the following or both:
Attorneys furnished by a bar association or a legal aid agency,
Attorneys furnished by a defender organization established in accordance with the provisions of subsection (g).
Prior to approving the plan for a district, the judicial council of the circuit shall supplement the plan with provisions for representation on appeal. The district court may modify the plan at any time with the approval of the judicial council of the circuit. It shall modify the plan when directed by the judicial council of the circuit. The district court shall notify the Administrative Office of the United States Courts of any modification of its plan.