It’s rewarded automatically for the main mission “Riptide” on moon Titan when playing as a Hunter. After the mission, you must speak with Sloane and can pick one of three exotics.
Exotic Name: Mechaneer’s Tricksleeves
Item Description: “This won’t end well for one of us. And darling, it won’t be me.” –Self-styled “Lady” Olu Alderdice
Special Ability #1: Spring-Loaded Mounting — Increases Sidearm ready and reload speed.
Special Ability #2: Increases this armor’s mobility, allowing you to move faster.
Acquired by: Beat the ‘Riptide’ main mission on Titan moon and you can pick it as a quest reward from Sloane (Hunters only).