parts for these 4th gen cars are basically non existent unfortunately, most have been junked or stripped for dirt track or cut up as donors for the front clips for classics and rods.
so next to none exist and no aftermarket companies took after them. youll have to get a hold of interior shops to have seats and such done for it. i think you can find new carpet for them but not much else.
it will be difficult.
i practically grew up in a 78 nova coupe when i was very little and i had a 77 and i always have wanted another one but damn none are left, literally. all gone now.,