Pls, does anyone know where I can get a brand new oxygen sensor in Lagos for my 2007 Mazda 6?

Pls, does anyone know how many oxygen sensor a 2007 Mazda 6i 2.3L Engine(4cylinder) has in all?

How do you replace oxygen sensor on a Mazda 6?
I have a 2005 Mazda 6s (V6 engine). There are 4 Oxygen sensors on my engine. You will need a special slotted socket wrench. It cost about ten dollars at your local auto parts store. It's designed with a slot in the side wall to fit over the wires coming out of the top of the sensor. On each side of the engine there are two sensors. One at the top of the catalytic converter and one in the pipe just below the converter. You go at the ones in the bottom of the converter from under the car and the ones in the top of the catalytic converter can be removed from inside of the engine compartment. You will have to remove the engine cover and the intake manifold to get at the sensor on the back side of the engine near the fire wall. Be sure and disconnect the connector of the oxygen sensor so the wires will not be damaged while you remove or replace the sensor. I'm sure if your car has a 4 cylinder engine you will have just two on the front side of the engine. One just below the exhaust manifold and just below the catalytic converter. Same procedures less work.

source: http://www.answers.com/mt/mazda-6

confirmed here: http://www.justanswer.com/mazda/5onlf-check-engine-light-o2-sensors-disconnected-battery-cable.html