FAdeA will deliver spoilers, flap fairings, tail cone, electronic cabinet and doors for the nose landing gear and ramp.
Aero Vodochody will build the rear fuselage section, crew and parachute doors, emergency doors and hatches, cargo ramp and fixed leading edge.
Argentina's government last year committed to order six KC-390s and the Czech Republic pledged to buy two.
But the LAAD 2011 show passed without Embraer securing new orders or signing agreements for other key suppliers, including the cockpit and engines.
The first KC-390 is scheduled to begin assembly in 2013 before first flight a year later and first delivery to the Brazilian air force in 2016.
Several companies are still seeking to gain position on the largest aircraft Embraer has launched to date.
Two Israeli companies - Elbit Systems and Israel Aerospace Industries - confirmed interest in competing against each other and perhaps others to supply the cockpit system.
Ran Hallerstein, executive vice-president and co-general manager for Elbit's Aerospace division, says the company has submitted bids through Brazilian subsidiary Aeroelectronica (AEL) for several systems, including mission system packages, electronic warfare suite and payloads.
The most challenging requirement AEL's bid faces is the Brazilian air force's demand for a commercially certificated avionics system.
Meanwhile, Yair Shamir, chairman of IAI, has not ruled out interest by the Israeli military for a KC-390 order.
"We will look at it," Shamir says.