Five or six speed? I’ve got a six speed Nardi knob in ‘as new’ condition which I promised someone several years ago I’d sell for them - for £5 plus postage. Love to get rid of it?
If its scuffed, easy to DIY refurbish, if its anything like refurbishing a worn steering wheel. Sand it smooth with 800 grade wet and dry, clean to remove any dirt, grease. Then use a black leather dye from someone like Furniture Clinic, seal with a gloss top coat (Furniture clinic also do an epoxy additve for high wear areas). Tone down the gloss with a satin coat.
I’ll spend 10 minutes with it with some sandpaper for £75. Honestly, if its just scuffed, its an easy fix, cost is about 10p plus whatever kiwi polish goes for. No need to pay anyone. If its ripped, bin it and buy a new one. Have you actually tried Mazda. Most Mazda dealers have access to the EPS and can order from a Roadster VIN. If its in stock in japan, it will be with you in 5-10 working days. The part number is M518-17-520A. The part was fitted to Eunos Roadsters 1992-1997.
Alan Gun in Florida used to refurb these Mazda Nardi knobs.
I would just buy a new one though, and pop out the thread insert from one of the scrap ones you have. I doubt anyone would charge less than £45 to refurbish one; likely, if you insist on new leather and stitching, its going to be £100+.