Oh, they come through Jubilife, but most of them travel from farther still! Johto, or maybe over the water from Kanto. It is their entire living - traveling with the guild caravan, selling their wares. The northern leg is a minor one, really, and only a few do it regularly.

[The Pearl Clan are reliable customers, though, and there's goods to be traded for there that you cannot find elsewhere.]

We do not see them at all after harvest-time, but they come by a few times a season before that.