Leopard V2 is obtained in the Leopard Dungeon found on teleport island. (First Sea) The boss inside has 100,000,000 HP. Chop is recommended for it's unique ability to negate sword damage.
Upon defeating the boss, you have a chance to obtain the Leopard scroll, which if right clicked while having leopard fruit equipped, grants you Leopard V2. The scroll grants you all of the moves Leopard V2 has.
Once you get Leopard V2, you can get Leopard V3.