It won't do any harm to try.
you can get those throttles anywhere, except you might need to adjust the wiring to suit the Freego.
the switch is basically independent of the throttle. the throttle used three wires, two of which power it with 5v, and the third is the signal back to the controller. One of those wire is routed through the switch. When you buy those throttles from Ebay or Aliexpress, they have five wires, so to wire them in the same way, you can cut the red 5v wire and join each end to the two wires from the switch.