I assume you mean the "special tool" ?
I got mine from ECS Tuning, but they no longer stock it.
Try
Mercedes Tools - Mercedes Benz Special Tools & Repair Information-Tool

A208 899 00 80 or 129 581 00 66

I think I'd go with the 129 one, it says 6 MM hex, which is correct.

( this one has it at $16.90 + shipping https://www.factorymoparparts.com/oe...hoCUOwQAvD_BwE )

BUT WAIT !!!

This one has it at $19.99 with free shipping !!!! https://www.eeuroparts.com/Parts/758...BoChZUQAvD_BwE