Zephyr Singer - Promo Pack (PMOM) from March of the Machine, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Lie Setiawan
• Card Text:
  Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for 1 or one mana of that creature's color.)
  Flying, vigilance
  When Zephyr Singer enters the battlefield, put a flying counter on each creature that convoked it.