Grub screw to hold arm in collar - Akito mk 1

I'm in the process of buying a Linn Akito mk1, but the seller has informed me "the grub screw to hold the arm in the collar is missing. You'll need this to set VTA."

I'm not sure what he means, having never seen the arm, but does anyone have an idea where such a screw can be sourced?

The seller understandably doesn't want to send the arm without the screw, and is having difficulty sourcing one, so thought I'd ask here.