Ahh, I found a forum thread with people discussing installing these exact bags into a Mazda3. They're not a 100% compatible fit so you need to drill a hole or two, but they're installable.
http://www.mazdaspeedforums.org/forum/f12/uhhhhh-air-lift-kit-1000-a-26986/
This is the exact model people tend to be using. I'm going to do some measurements of my springs to see if things match up at home. https://www.amazon.com/LIFT-80754-1000-Rear-Spring/dp/B001OMVCTG/ref=au_as_r?_encoding=UTF8&Make=Mazda%7C80&Model=3%7C2435&Year=2008%7C2008&ie=UTF8&n=15684181&s=automotive&vehicleId=1&vehicleType=automotive