To buy all the weapons in the game world of RDR 2 in a regular store will not work. In the game there are different secret samples that are available for collection. So, if you miss them, then it will not be able to collect all secret weapon. Unfortunately you will not be able to find a new kind of weapon, but nevertheless will get the unique model of revolver, revolver, etc.
Secret weapon in Red Dead Redemption 2 need in order to completely fill your fighting Arsenal, but some species are still difficult to find. Some weapons you will get, if you win their opponents. In the game there are 5 characters for duels, each of you can challenge. These duelists will be a special weapon.