The Wings of the Amber Monarch cosmetic back piece that we previously covered has been updated with a 999x Trader's Tender cost likely indicating that it'll be a monthly Trading Post Traveler's Log reward similar to Grotto Netherwing Drake or Ash'adar, Harbinger of Dawn.
The Monarch Wings cosmetic back pieces come in 3 other colors (Wings of the Emerald Monarch, Wings of the Tourmaline Monarch, and Wings of the Amethyst Monarch), however, it remains unknown how these recolors will be obtained.