Caravans

Caravans are mini structures that spawn randomly across the world together with a bunch of villagers and their marine protection, sometimes these can spawn with vice admirals or pacifistas as guards along with the usual marine grunts.

The loot is guaranteed to have devil fruit boxes (any of the 3 kinds) when the caravan spawns with a vice admiral guard. However even without a vice admiral they still have a chance to get a wood or iron devil fruit box at a much lower chance.