The Athleisure Assassin skin is an Rare Fortnite outfit. Athleisure Assassin was available via the Item Shop for 1200 V-Bucks and you can buy it from Fortnite Item Shop when it will listed.
Fortnite Athleisure Assassin Skin Details
Definitely not off-the-rack.
Fortnite Athleisure Assassin Skin PNG Images
Here is the PNG images of Athleisure Assassin below!