There are currently 7 different Villager Outposts which generate throughout the Overworld. The design and location of Outposts are based on a Villagers type. Within an Outpost you'll find Village loot as well as a special Trader at the top of each Outpost. This Trader has different trades than normal Villagers. They're based on the type of the Villager. A Snow type Villager for example sells Ice Blocks. In addition to that those Traders also sell 2 of 57 Miniblocks as well as 1 of 183 Mobheads. All of those have noteblock sounds attached to them. Mobheads and Miniblocks are chosen randomly when the Trader spawns.