Magatama location?

[Lily]

would anyone know where to get these?

[qqchurch]

I somehow got two of those each while mindlessly killing some Pain Darumas in the West open fields in Kumaso. Though, I have no idea if there'd be a more reliable mob to farm, since I only got those within the 3 hours I wasted killing the same three mobs.

[SeekerFate]

The glass marbles can be found in any open field mob from anywhere up to izumo field or so the Japanese wiki says anyways.
I myself got a black glass marble from pendelga (whatever the floating snake things are in izumo).