This gun cannot be obtained by legitimate means in Borderlands 2. Pepperbox can only be obtained through third party programs or by trading with someone who hacked it into their game. This form of the Pepperbox was able to have an elemental effect.
The Pepperbox was meant to be the title of any Jakobs weapon that used the Vladof barrel. It was cut from Borderlands 2 presumably due to having an increased fire rate on a Jakobs gun being pointless, as players could not achieve higher fire rates physically on most Jakobs pistols anyway.