3 or 4 speed rotary or chain selector switch

As some of you know I just built a shop air cleaner using a 4 speed furnace blower.
I thought that is would be easy to find a simple rotary speed selector switch to control the blower speeds.
I was very wrong.
I looked in the Internet, Mc Master, Grainger, Amazon and my local hardware stores, I cannot locate one of this switch.
I ordered on Amazon a 3 speed fan switch, I received it yesterday, It has only 3 wires.
I just called the company which sales it, it will give 3 speeds only with their fan.

Do you where I could find one of this switch?
Thank you.
Bertrand

-- Bert