All evolve-by-trading-with-item ... items get consumed. Magmarizer included.
As for how to get more, apparently you can buy them in Black City (according to Serebii, at least), and there was an infinite number in B/W 1 from the treasure hunter on Route 13. --- If you actively hate Justin Bieber... then you don't know what "intended audience" means. Hate Twilight instead, it's far worse.