an 85 pickup is called the "720" fyi. There are alot of old 720's still running around. I imagine they are pretty stout. Nissan probably still keeps most important parts available. Some stuff like trim, etc might be getting hard to find.
I have no problem getting parts for my 81 210, you won't find anything in stock, but nearly everything can be ordered. I've never tried the dealership, but they probably can still get parts if you want to pay a lot.