You have two options here, create your own, or call one that is used in the encounters.
Which points to
mods\stonehearth\data\shops\basic_resource_shop.json that you can copy and modify to list the purchasable items you want.
tier_2_shops folders, which contain the json files for the traders that pop up periodically throughout the game.
- Level 1 Traders
- Stone Cutter
- Wood Cutter
- Level 2 Traders
- Weapons and Armor
Because they are called through campaigns, they aren't listed in the manifest file, so they don't have a uri to put into your market stall json file. You will have to create a manifest entry for each one you want to use, and then use that uri to call it from the market stall.