The Outlaws Is Coming (1965) on Netflix

Larry, Moe, and Curly Joe work for an editor at a Boston wildlife conservation magazine. They make such a mess of the pressroom that their publisher gets rid of them by sending them out west to stop the slaughter of buffalo. Upon their arrival they find themselves being sought after by every notorious gunslinger in history, including Wyatt Earp, Wild Bill Hickcock, and Jesse James. Luckily, pistol-packing Annie Oakley, who has fallen in love with the handsome editor, agrees to protect them against the bad guys.