There is only a single location where players are able to purchase Shallots in Bulk. Shallots are sold by Ichtaca in Timberline Falls. 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.
The Renown Heart Karma vendor, Ichtaca can be found in southeastern Timberline Falls just north of Nonmoa Lake. The closest Waypoint is Eztlitl Grounds Waypoint.