You go the tune shop where you buy parts. Go to ENGINE & INTAKE SYSTEM. Once you go in there it's under N/A TUNE UP/ STAGE 3.
I'm not sure if you can buy it on the Miata, but it's worth a shot.
Also, do these if it's possible: Racing flywheel, carbon fiber drive shaft,full racing transmission, all of the lightening stages,triple plate clutch, race exhaust,race chip,port & polish...