Update on the OMP Champ-R bucket seat, it wil fit in a NA Miata with some custom brackets. But be careful if you're around or above 185cm you'll won't have enough legroom. :) :
NC Adjustable NC MX-5 Seat Mounts - Garage Star
CYBUL Radical Solutions - MX-5 NC roll bar & bucket seats are in! Do you like the design? We managed to make it work with windshot :) // Rolka i kubły ładnie
Corbeau Forza Fixed Back Seat and Slider Installed on the NC Miata - YouTube
NB] Will bucket seats give me more space? - MX-5 Miata Forum
Racecarsdirect.com - Mazda MX5 (NC) Track Car
How to install bucket seats and harnesses - Mazda Miata - YouTube
Bucket Seats In An Nc Talk To Me (Rodders, Blink Etc) | Mazda MX-5 Miata
Love the roll bar, Sparco seats and harnesses in this MX-5 | Mazda mx5 miata, Miata, Mazda roadster