Where can I get a Control Board for Ducane Furnace Model MPGA100B4A? My tech cannot find one?

Your unit

http://www.mid-lakes.com/pdfs/ML_06_..._Section_6.pdf

This company wholesales the part you need. They probably will not sell it to you but they will steer you in the right direction to buy it.

All parts are available for your unit.

Mid-Lakes Distributing
1029-37 W. Adams
Chicago, IL 60607
Ph. 312-733-1033
Toll Free: 888-733-2700

Honeywell and White Rodgers also make a board that will work in your unit. Honeywell is OEM on the fan control side.