I recently fitted a Sparco Sprint V to the passenger side of my NB8B.
I had to make up adapters to go between the seat and the rails, so I referenced the design of the Jass performance ones since you can't buy them here and just made some myself.
I couldn't find much information on the internet while I was making these so I may as well post the info I have to help others trying to do the same thing.
Here's the design if you want to bang some up in the shed, you'll just need:
2 pieces of 50mm x 5mm flat bar, 355mm long
4 M8 countersunk high tensile bolts
The circles that have an extra circle around them need to be countersunk from this side, don't countersink too deep, just enough so bolt head is flush.
I welded nuts onto the other side of the plates behind the non counter sunk holes, but you don't have to do this, Jass used studs, you can just use stock bolts + nuts and get a spanner + shifter in there.
The holes on my design say 9mm, you will actually be putting 8mm bolts in but the 1mm of play allows for a bit more leeway.
You can cut the middle bits of your adapters like the Jass ones to save some weight.
Here is the Jass brackets
(This image has been flipped as the design was created for left hand drive cars, this flipped image is how it needs to be on right hand drive cars)
Good luck
tags for google: nb8b mx5 mx-5 miata roadster passenger bucket seat rail adapter sparco sprint v
