The blackjack seller is a man in the town centre of Pollnivneach that sells blackjacks. He is just south of the kebab shop. The Blackjack seller is constantly having his products stolen by the street urchin.
The completion of The Feud is required to access the blackjack seller and his shop. This quest can be started in Al Kharid.
Ali Morrisane has a business proposal for him during the Rogue Trader miniquest. After the player convinces him, he will start shipping offensive and defensive blackjacks to Ali Morrisane in Al Kharid. He will also sell a willow-blackjack to the player.