speed warning speedometer parts

[72 K20]

Hi ! I have a speed warning speedo in a cluster that came in the last 72 that I bought. The speedo is there with the offset needle and the white needle. But that's all there is,,, the bezel has the hole where I assume there was a knob or dial to set the warning needle . From what I have read there should be a buzzer or something on the back side of the bezel.
Is there anywhere to get these parts ? Wasn't the speed warning a 69 year only option ? I don't know a lot about these ,, and don't really have any plans on restoring it unless the parts to complete it are very affordable .

Thank you in advance for any and all input ! Have a great day !!!
Tom