Mazda bits? We've got coilovers now, but I'm sure we can do poly bush kits and such so I'll see what else is available
There's a whole bunch of things which are quite hard to get hold of at the moment but when they come up for sale they fly out.
Obviously, decent sidemounts for bucket seats
FatCat suspension topmounts - these raise the centre of the topmount to give added suspension travel without raising ride height
Steering bits - Plenty of OEM spare stuff but nothing really aftermarket in the UK. Beefier track rods with more thread/buit in spacers to achieve more lock. Maybe with a kink to clear the upright. Should be easy to increase the lock on these cars but it's expensive to do it properly and really hard to get good bits to do it.
Bushes - poly bushes aren't that hard to get hold of but there's always a market for them. Not just wishbones and ARBs, but also diff mounts, power steering rack mounts, that kind of thing.
Bracing parts - there's a bunch of chassis braces which can be added to the Roadster to make it a much better car. Obviously strut braces, but also a few for the subframes. Then there are more unusual ones, like the Boss Frog braces for the front chassis legs, and I think Tein do a Diff brace which ties it into the rear subframe. None of these things are particularly hard/expensive to fabricate, it just looks like nobody is doing it currently.
If you're able to supply them, Axxis Ultimate brake pads are the, uh, ultimate brake pads for the Roadster. Currently they're a bit tricky to get hold of.
There's lot of other bits I'd love to see available like flush headlights, that kind of thing, but as your'e not an MX5 specialist I don't think any of that is very likely. But the bits listed above would sell well and are the really worthwhile bits to add to a Roadster, along with good shocks etc.
I'm happy to provide more info if you need anything else. PM or email me if you want.