I've had really good luck with my local junk yards. I also check Row52.com to search for anything that might be 3 hrs or less for me to travel and get stuff I need. Craigslist is also a really good source for complete parts cars. I found this 89 CS International coupe 3 hrs from me and it's currently proving to be extremely valuable for all the things I need to fix up my 91 CS International coupe.
If you can find a parts # book for the Z34, those are great too. I have one for each of my cars and you can use them to find the part #'s you need. I then call up my local GM dealer and they can use the part # to find NOS parts throughout the U.S. and Canada. I've found a lot of rare NOS stuff that way.
Getting back to the parts car, I only paid $300 bucks for it if I remember and I can't tell you how much time and money it has saved me trying to track stuff down. Try to find one that's damaged or really rusty like mine is which makes them cheaper to buy and easier emotionally to part out. Depending on where you live, you might have to travel a ways to find a parts car that wasn't subjected to interior Sun damage. I'm in the Midwest so our car interiors don't suffer from that sort of thing. Interior components that cannot be swapped over from a parts car can be restored depending on what you need done thru upholstery shops and such. Some things like carpet and headliner material can still be found on the Internet.
Hope this helps and please post some pics! We love the Z cars!