The ones on the car are quite standard aftermarket ones tbh, and are not the best quality, but are still what is widely found on the marketplace. Not terrible quality, but not perfect.
I do have a genuine set of early 240z fibreglass buckets spare, and they are immense in quality and thickness!!! Very heavy too!!! I need to set some new studs in them as I had not had time to do it as of yet, and then I can have those as spares. The original studs had been snapped so I drilled them out. I just need to put new studs in.