Best way to earn Pig Iron and Birdium?
I'm finding it rather difficult to earn sufficient Pig Iron and Birdium.
From what I've seen they're only available in the Easy and Medium missions, mainly in the 4h and 8h missions, and even then in generally small quantities.
And yet for the L12-L13 upgrade we need 50 units, and for the L13-L14 upgrade we need 60 units.
And there are no recipes that allow us to convert other materials into Pig Iron or Birdium.
In contrast, it doesn't seem nearly as difficult to earn DG/AG or BP/AC especially since you have the ability to convert "lower level" materials into "higher level" ones, and relatively speaking you don't seem to need nearly as much BP/AC to upgrade (although I suppose you could suck them away fairly quickly if you're converting them to SR and gems).
So how are people managing this?