pulse generator

Hello,
I am setting up a stepper motor to drive a mechanism at variable
speeds, 0-60 rpm Spec sheets for the motor and driver can be found on Anaheim Automation web site, the motor model is 34Y214S-LW8 and the driver model is MBC10641. The tech support person at Anaheim Automation advised me that I would need to purchase an external "pulse generator" in order to make the setup work as I would like. I need to be able to change the speed of the stepper motor on-the-fly without having it connected to a computer by simply turning a knob such as on a potentiometer.
He told me I would be able to pick up a pulse generator from Radio Shack, however I was at the store and they were not too helpful.
Any assistance would be appreciated.

Sincerely,
Denis