KELP

Kelp 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 3 emeralds each.

Kelp comes from ocean and river environments, so unless you live on the coast it usually means a dedicated expedition. Trading skips that trip entirely. No recipe in Java 26.2 produces it: it comes out of kelp plant.

The Wandering Trader sells Kelp for 3 emeralds each. He does not buy kelp back: that offer runs one way.

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

He asks 3 emeralds each, and 58 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 kelp is the real constraint.

The Wandering Trader asks 3 emeralds for kelp. 8 of the 72 villagers that pay emeralds, emptied out:

3 lava buckets against 90 flint for the same 3 emeralds, 30 times the carrying, and the shortest wait is the Shepherd at 1.9 real minutes 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 kelp. He takes six kinds of item and this is not one of them, so the offer runs one way: emeralds out of your inventory, kelp 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 kelp 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.