Mother 3 ultimate equips locations

Depends on your play style.

Lucas' Final Armor is the Awesome series which you can find in the Bathroom Dungeon (Ring), the Final Cave (Bat)

Kumatora's Final Armor is uh... mix-matched which you can find it Construction Area(Gloves),

Boney's is the Lab(Canine Weapon)

Duster's is in the Hippo Room(Shoes)

I managed to beat it on that, so you should be able to.