The Stockmen's Association is a faction in New California in 2241.
Background
The Stockmen's Association is an alliance of wealthy brahmin barons operating in New California. The organization's head, Duppo, operates the entire enterprise from the NCR capital in 2241.
Interactions with the player character
The Chosen One can go on a cattle run for Duppo, indirectly working for the Association.
Appearances
The Stockmen's Association appears only in Fallout 2. While not explicitly mentioned in Fallout: New Vegas, it can be assumed that it is still active, judging by the significance of brahmin barons in 2281.