March Size Increase items come in Junior/Medium/Senior tiers. Free/event sources: Viking Event Viking War Chest may give any tier (lucky). Dawn of Civilization top ranking: 1st = Senior x10, 2nd = Senior x6, 3rd = Senior x3, 4th-100th = Senior x2. World Boss personal-damage ranking: 1st = Senior x3, 2nd = Senior x2, 3rd-10th = Senior x1, 11th-50th = Medium x1, 51st-100th = Junior x1. Tsarevich Egg (needs Civilization Treasure Faberge Egg Lv2+): from Lv10+ resource tiles, may give one Medium if lucky. Maria Egg (Faberge Egg Lv3+): from Lv15+ tiles, may give one Senior if lucky. Paid: Auction Rare Goods Senior lowest 55,000 gems; Store Senior 100,000 / Medium 25,000 / Junior 8,000 gems; Event Package 4th ($49.99) = Senior x1, 5th ($99.99) = Senior x3; Battlefield Shop Battlefield Super March Size Increase = 25,000 gems. For a bot, march size directly raises troops per gather/attack; earn increases free via rankings (Dawn of Civilization, World Boss) and Faberge-Egg tile drops rather than paying.
Original research source: Evony Guide Wiki