I was digging for fun stuff and ended up finding a header for the 1.2L 3A92. The blog post is from June 18, 2015, so its a fairly recent development. No idea of the build quality nor do I have any reviews on it, but it does look pretty nice. The dyno chart they provide a picture of is a little odd. It has 3 separate pulls on it so you don't know really what is what. I never saw a picture of the stock exhaust manifold, but it does look pretty horrible haha.
SuperCircuit is a company in Malaysia. I'm going to email them about a price shipped to the US so we have some idea. SpeedLab quoted someone here I think $250 (currently $180 USD) shipped to Australia.
Here is the email reply from SuperCircuit:
Mitsubishi Mirage (6th Generation) HeaderThe SUPERCIRCUIT 3-1 Headers made for Mitsubishi Mirage 1.2L is USD237.00 each.
It will be an extra USD70.00 each for the delivery via Post Office's EMS. The normal leadtime will be around 15-20 working days to arrive your doorstep.
blue = stock
red = Supercircut header
green = Supercircuit header plus 2ndary CAT removed