Suspension hardware is made by a handful of companies around the world.
Everyones seen those pictures of the threads on a sleeve wearing thin and the thing breaking etc.. Rare.com
When buying suspension you shouldn't worry about anything except how long this $1k+ hardware is going to last, how it performs, and who'll fix/replace it when it breaks!
Therefore, I stick to the majors w. the network to support my usage.
The miata is a rare car where a fancy pillow ball bling coil isn't needed.. granted you we need travel but either a shorten shock, ext travel mounts, or something with adjustable bodies will do..
Besides a circuit only "race" system $2K+..
A set of Koni race (already shortened)- $1k
GC's (w. your own spring rates) - $400
=$1400
Will be the best thing you can buy.. and servicable in the US.
OT/kinda,
I have a rally friend who was getting replacement KYB's after every race because he'd blow them (DUH) and usually they'd be broken. The guy replacing them knew this..
Try that w. something imported/rare.