Where can I buy a Honneywell circuit board ST9120C

Here is a couple place, if you merely place the part name in a Yahoo search dozens of places pop up.

Furnace Fan Timer # 1170063/ST9120C 5013 (http://www.myhvacparts.com/Catalogue/Printed%20Circuit%20Boards/Comfortmaker%20Control%20Board%20ST9120C3000.htm)

https://keithspecialty.com/hvac.parts.Honeywell.htm