You get it by capturing a magby in your Pokemon Diamond or Pearl. You do the insertion trick with Pokemon Leafgreen, and you can find Magby on route 227 and on Stark Mountain. In Diamond, Magby have a magmatizer about 5% of the time. In Peral, Magby have a magmatizer about 50% of the time.
That's in the route south of Veilstone.
right after you go into stark mountain you run around until you eventually find a magby,catch it and it might be holding a magmatizer.
Catch a wild magby
Yes, on cinnabar island, just explore the island that the pokemon center is on.
route 214 near cave need rock smash.
put a female electricc Pokemon and a male ditto in daycare together then wait go to the bald guy he gives u a egg and its elecid evolve to electrabuzz get the magmatizer from prof oak in shaymins field and give it to him he evoves into magmortarr