gear 2

gear 2 is easy to get all you have to do is kill a boss, any boss in the whole game has a chance to drop. but the higher the level of the boss the higher chance it has to drop.  (min: 1.5% max: 7%) (you must have rubber fruit active)

gear 4

gear 4 is kinda hard to get, its a 2.1% drop from the new luffy boss located on the new rocky islands. the second strongest enemy in the whole game. (you must have rubber fruit active.)

suggestions

i recommend you farm the yeti boss for a 2.7% drop chance of gear 2 every time you kill him but he is located in second sea so you need a mimimum of level 105.

and for gear 4 I recommend you are level 220 with all your stats for fruit applied and that you have every type of haki.