Where are the Russian Axe & Ararebo Melee Weapons???

While it is unrelated to base game, Ararebo became available in Incursions to people who completed 3 competitive matches since the update that introduced it. There is no information on what the requirements for Ararebo will be in retail though (even if it shows as a puzzle piece weapon now, things might still change), although it wouldn't surprise me if in the end it somehow ended up being related to Incursions too.