Each March of The Machine: The Aftermath - Epilogue Booster Box contains:
• 24 March of The Machine: The Aftermath - Epilogue Booster Packs • 5 Magic: The Gathering Cards Per Booster Pack • 1–3 cards of rarity Rare or higher and 2–4 Uncommon MTG cards in every pack • Guaranteed foil and Showcase card in every pack
Starting with The Brothers' War, Buy-a-Box Promos will only be available for in-store pick-ups and purchase while supplies last as stated in Wizards of the Coast's article here.