m3sakura has the exact same quality shell, but suposedly with a side-loaded microSD slot.

shells from other flashcard might work, depending on the exact version of m3real and what the donor is.
i think most shells will work if you got one with a flat chip, otherwise you need the shell from another flashcard with a fat chip..

empty shells are not for sale, so you're best off with the shell of a fried m3real.

altough i can only think of 2 ways to really break the shell of your m3real.
either by taking it apart too much(clips might break off), or by dropping something heavy on it(like a stone, or a foot)