FERN

Fern is a Wandering Trader exclusive: no job villager buys or sells it at all, so the roaming merchant with the two llamas is the only source, at 1 emerald each.

Fern is a landscape block, so the trade is really paying for the trip to the biome that has it. No recipe in Java 26.2 produces it: it comes out of large fern.

The Wandering Trader sells Fern for 1 emerald each. He does not buy fern back: that offer runs one way.

No standard villager profession lists Fern in its trade table, so the trader above is the whole market for it.

He asks 1 emerald each, and 30 of the other 75 come cheaper. Price is the easy part: he draws his stock from a shared pool, so catching one that happens to be carrying fern is the real constraint.

The Wandering Trader asks 1 emerald for a fern. 8 of the 72 villagers that pay emeralds, emptied out:

a jungle boat against 26 flint for the same 1 emerald, 26 times the carrying, and the shortest wait is the Butcher at 37.5 real seconds of shelf, gathering not counted.

The Wandering Trader is not part of any village. He arrives on his own near where you are playing, with two leashed trader llamas behind him, stays for roughly forty minutes to an hour, and then vanishes whether or not you traded with him. There is no workstation to place and no job block to break, so the usual tricks for steering a villager toward a particular offer do nothing.

He does not buy fern. He takes six kinds of item and this is not one of them, so the offer runs one way: emeralds out of your inventory, fern into it.

Each trader carries only a slice of the full stock list, so the one standing in front of you may simply not have fern today. If he does and you want more than one visit's worth, put a name tag on him: a named mob will not despawn, which turns a passing merchant into a permanent shop you can come back to.