This should be obtained naturally as you will find you'll be having to Parry a lot of attacks sometimes, especially from dual wielding Cyborgs or Custom Cyborgs as they can attack many times in a row, also some battles you will be facing large groups of enemies. It's key to remember that to parry you need to move your stick in the direction of the incoming attack and press square, this is a vital skill to learn through the game so you'll find this should come naturally. If you are having troubles you can fight Monsoon as his smoke bomb attacks are easy to parry and there are enough of them to get this, also his regular combos can be up to 10 attacks alone and offer an opportunity when he unleashes on you.