U cant you have to goto pal park and trade it from the GBA game to diamond.
This is mawile
You must transfer registeel from a GBA game to your diamond/pearl game in order to obtain it.
you need to trade it from ruby
You don't. to Get any of the regis on Diamond, Pearl or Platinum, you would have to trade online with someone who does have one or get it from a Pokemon Ruby, Sapphire, Emerald, Fire Red or Leaf Green
I do not believe there is a mawile in sapphire. Otherwise no i don't know where to get one!
I think there are Mawile found south of Mt. Pyre (Route 123 to the west)
I have beat the game and have not found any trainers with a mawile.
Steel type
In the National Pokedex in Pokemon Platinum Mawile is Pokemon 303.
'Mawild' is most likely the Pokemon Mawile (sometimes mispelt as 'Mawhile'). Mawile is a Pokemon available firstly in Ruby but can be obtained through slightly normal gameplay in Pokemon Diamond and Pearl. It is a Third Generation Pokemon who is of the Steel type. Mawile can be recognised by it strange horns protruding from its head, which take the shape of something resembling a gaping mouth. Mawile currently has no evolutions or pre-evolutions and is generally an average Pokemon stat-wise.
It can be captured at victory road.
You have get Pokemon ruby and then get it and trade it to Pokemon sapphire. hope i helped!!!