TWO SPEED 10 HP MOTOR

You might want to try an engineering search engine like this.

thanks for the info.

Use a 10hp inverter duty (EE) motor and a VFD. The VFD can be programmed for "preset speeds" switched by a relay/relays. This gives you the flexibility to dial in the exact RPM/CFM you require. With a 2-speed motor you get what you get (typically 1800/1200 RPM). By the time you find a 2-speed 10HP motor (rare these days & expensive) and the starter (also very pricey) you are time and money ahead using the VFD. Welcome to the 21st century!

FYI: I am assuming the makeup air unit has a forward curve fan (most in this size range do). I am not sure you can turn a 12875 CFM blower down to 4900 CFM and be stable. Check the published fan curve. Have fun!