DISCS:

Creeper: stal, cat, 13
Dungeon: stal, cat, 13
Bartering/fortress: Pigstep
Fishing Treasure: Wait
Fishing Junk: Stal
Desert Pyramid: mall
Shipwreck: wait
Jungle Pyramid: chirp
Buried Treasure: cat
Stronghold Crossing: ward
Stronghold Library: Blocks
Mansion: far
Villager: Mellohi
Wither: 11
End City: Strad

BANNERS:

Thing: End city, wither (RARELY)
Globe: Wandering Trader/stronghold library
Flower: Master Cartographer
Skull: Fortress/buried treasure
Creeper: Dungeon
Snout: Bastions (like normal), piglin bartering

I also wanted to make them renewable so you could still obtian them when playing with structures off:
As mentioned, Flower can be purchased from a master level cartographer (instead of globe), snout from piglin trading, buried treasure is a feature not a structure, and thing as a VERY rare drop from the wither. As of now, creeper would be unobtainable in these challenge worlds, but I am open to suggestions.