Mazda's got a much smaller piece of the pie, so performance upgrades are not as likely to surface as other manufacturers. From a numbers perspective, it doesn't make that much sense for a company to spend hours of R&D on a vehicle that's sold 2500 units across North America, vs spending the same number of hours on a vehicle that's sold 10000. If they were to do it, it would be low priority.
That said, some users here have stated that one of the 2nd gen CX-9's weak points is the brake performance (when pushing the CX-9 around canyons/mountains). PBbrakes.com is one option.
Front BBK:
http://pbbrakes.com/brake-kits/mazda/cx-9/mazda-cx-9-16-up-front-big-brake-kit.html
This kit comes in different configurations from 6-pot to 8-pot calipers and 345x32mm to 430x36mm rotors.
Rear BBK:
http://pbbrakes.com/brake-kits/mazda/cx-9/mazda-cx-9-16-up-rear-big-brake-kit.html
This kit comes in different configurations from 4-pot to 6-pot calipers and 330x28mm to 405x34mm rotors.
Each kit comes with SS lines, and you have a lot of customization options like brake pad type, paint colour and finish, and different rotor options like drilled, slotted, drilled and slotted, as well as fixed and floating rotor options. The front and rear kit is not cheap at $3578.58 + shipping to start, but it seems to be the only option at the moment.