The April Patch Notes say:
Added new rare apparel drops:
Toxic Aerofin Apparel - Murkwood/Peaceful Pond
Abyssal Aerofin Apparel - Darkspine/Backwoods Brook
Icy Aerofin Apparel - Icerun/Frozen Fjord
Volcanic Aerofin Apparel - Goldsea/Open Ocean
This has led the community to believe they also drop in Campaign, but they don't appear to be listed as drops from any companions and there are no new encounters
@Quiche I imagine you/devs are the only ones who can answer this.. can you confirm they are available in Campaign and if so, how they are acquired?