(a) Where without fault of either party the agreed berthing, loading, or unloading facilities fail or an agreed type of carrier becomes unavailable or the agreed manner of delivery otherwise becomes commercially impracticable but a commercially reasonable substitute is available, such substitute performance must be tendered and accepted.
(b) If the agreed means or manner of payment fails because of domestic or foreign governmental regulation, the seller may withhold or stop delivery unless the buyer provides a means or manner of payment which is commercially a substantial equivalent. If delivery has already been taken, payment by the means or in the manner provided by the regulation discharges the buyer's obligation unless the regulation is discriminatory, oppressive or predatory.