In 1966, the American Character Doll Company released four action figures based on NBC’s Bonanza: Adam, Little Joe, Hoss and the dastardly Outlaw. There were also horses and a 4-in-1 wagon available. The now-defunct Bonanza World website suggested that the Outlaw figure was originally supposed to be Adam but after Pernell Roberts left the series it was reworked so the company could still sell it. VintageDollCollector.com has an extensive overview of the various dolls sold by the American Character Doll Company; apparently the Bonanza figures were the only action figures the company ever released. Judith Izen wrote an identification and value guide called American Character Dolls that was published in 2003. I don’t know if it mentions the Bonanza figures.
These figures, some loose, some with their original packaging, can occasionally be found on eBay.