So I'm assuming you want a Steel type and one more Pokemon. Your current STAB moves leave Normal, Poison, Ghost, Electric, Psychic, and Fairy uncovered. Alolan Dugtrio would cover Poison, Electric, and Fairy super effectively with its STAB. It's easy to obtain, quite powerful, and fast.
Dugtrio-Alola @ anything
Ability: Tangling Hair
- Iron Head
- Night Slash / Shadow Claw
- Stone Edge
Now you only have Normal, Ghost, and Psychic uncovered. Pangoro can cover all these types with its STAB. It's decently easy to get (you will need a Dark type to evolve Pancham, but those are everywhere), and it has a gargantuan Attack stat, perfect for in-game.
Pangoro @ anything
Ability: Mold Breaker / Iron Fist
- Brick Break
- Poison Jab / any other physical move
Hope I helped!