HOW CATALYTIC CONVERTERS ARE THERE? CAN I USE AFTER MARKET & STILL PASS SMOG?

Yes you can use an aftermarket Catalytic Converter and still pass smog, it just needs to be the correct one for the vehicle with the part number and EO number stamped on it. If it fails and isnt replaced it will increase the emissions and in severe cases where it gets plugged other issues could arise from the engine.