No C (Common) terminal on Furnace.
Take the blue wire from the cable to the thermostat, nut it with the two blue wires in the foreground, done

The two blue wires in the foreground of your first two wiring shots are both C wires -- the thick is the C wire coming from the furnace, while the thin one is the C wire returning from the air conditioner compressor (it's the one that goes into the cable where the yellow wire was the only other wire used).  So, you can simply strip the end of the blue wire in the cable to the thermostat and include it in the junction with the two existing blue wires up front.