C wire for Ecobee3 thermostat in 2 zone heating and A/C
Looks like there's an extra blue wire in each of the thermostat cables at the zone controller. Simply connect the blue wire from the thermostat cable, to the C terminal of each ZONE# T'STAT terminal block. Then connect the blue wire to the C terminal on the new thermostats. This should give you power to the thermostats.



However, since it looks like it's using the transformer from the air handler to power the zone controller. You'll likely have to also install a jumper from the C terminal on the 24VAC Transformer terminal block, to the C terminal on the System terminal block.  



Depending on the transformer that's in the air handler, the additional load of the thermostats might be too much for it.  So make sure the secondary side of the transformer is fuse protected. If it is, and the fuse blows. Then you might have to upgrade the transformer, or use a second transformer to power the zone controller and dampers. 

WARNING: If the transformer is NOT fuse protected, and you draw too much current. You will end up damaging the transformer.