There is only a single location for players to purchase Green Beans in bulk and it is from Albin Chronicler who is located in Wayfarer Foothills. Now before I get started with telling you the two locations keep in mind in order to purchase any goods from a Karma vendor you must first complete the quest they have for you. That is of course if they have a quest available if not you'll be able to buy whatever they're selling right away.
Albin Chronicler is located in The Icesteppes of Wayfarer Foothills which is in the central part of Wayfarer Foothills. The closest Waypoint to Albin Chronicler is Zelechor Hot Springs Waypoint. There are two Renown heart NPCs in my picture below of the Waypoint, the one you want is just to the right of the Waypoint's text and is the only filled in heart.
For further clarification: