Help, ran out of Beginner Black Stone (Weapon)

Here's the gist of it. My luck has been completely shit. Stock is blood red, GameZ's cash stuck in limbo, and I FAILED TO PEN MY NARU SHIELD. I've completed both Calpheon and Media main quest. They gave me enough beginner stones to PEN almost everything. Had almost 1k stone left for the Naru shield, but then it just. keep. failing. I even used my valks just to PEN it. So now I'm stuck with a PRI Naru shield that I can't trade in, and no more beginner weapon stones. I tries converting normal black stone into beginner, but the exchange rate is a ludicrous 3 normal stone for 1 beginner. So I'm I fked or is there a secrete way I can get more beginner stones.

 

Apparently the secret is effort. You can grind for them.