Unfortunately, Rockstar Games hasn't released any big DLC for Red Dead Redemption 2. The game had great potential, but the developers decided to only release multiplayer content. Fans decided to fix this problem by adding items from Red Dead Online to RDR 2.
The Red Dead Offline modification adds Red Dead Online content to the single player mode. The items will be available from various merchants, and can also be obtained through a trainer. The modders have spent a lot of time making the content fit well into Red Dead Redemption 2. For example, some of the weapons will be available at the beginning of the game, while some samples will only appear from selected merchants as the story progresses.
The mod adds clothing, holsters, saddlebags and saddles, new weapons and their customisation, ammunition and more to the game.