Missing BALL 3M, 1/2, Out of stock on lego.com

Hello r/lego,

I started building sets in my backlog with my kid. It's a cool father/son bonding time.

Now, him being 2 1/2, he obviously sometimes lose pieces. It happens. I usually replace them with spares I have around. But for the 75021 Gunship, I need to replace one of the BALL 3M, 1/2.

Brick Color DK. ST. GREY

Element ID 6037804

Design ID 44359

It's out of stock on lego.com. Any recommendations to find the piece somewhere else?

Thanks!