where i can buy a stepper motor gear like this

attached a gear that fits perfect what i’m looking for to develop a follow focus with arduino,
i want to connect the gear with a stepper motor but i can´t find a gear like that,
the stepper motor shaft is 6mm
thanks a lot

A blurry picture of one side of a gear is not sufficient. You need to determine the specifications of the gear: tooth count, pitch, pitch angle, width (total and just the geared part)... Take the gear to a gear distributor and ask them for a matching gear.

I believe that is a pinion gear. You need to specify the stepper motor shaft size and number of teeth on the gear.

Shaft is 6mm or 6.35mm??

hi sorry for delay, shaft is 6mm thanks

Go to any machine shop. They'll make it for you but it probably won't be cheap. Alternatively ask any of your friends that may have a lathe and dividing head.