The wonderful thing about a Jeep is that there are parts out there for any year and for parts that aren't available there are adapters for a newer replacement part. I wouldn't be afraid to buy most Jeeps that have the essential parts in working order or are intact.
Make sure the frame isn't rusted through or cracked.
Make sure the floorboards are intact. (Meaning you aren't looking through to the ground under the driver or passenger floorboard.)
Make sure it drives straight down the road not like a dog trotting down the road sideways.
Listen for rear end whine or front end clunk when you're turning at low speeds.
Check the fluids to see if they look okay. Antifreeze that has oil floating on top could be serious engine problems. An automatic transmission fluid should NOT smell burned.
Listen for engine knocking. That could mean a spun rod bearing.
I guess this list could go on but listen to that internal feeling of this is okay or RUN!!!!
Even if you did get a Jeep that isn't in the best shape, this forum and others like it have loads of good information and help to bring a not so good Jeep to up and running reliable condition.
I had a '48 CJ2A for over ten years and didn't have any problems finding parts. I was just young and didn't have the money for the parts. I also had an '85 CJ7 that was in pristine condition. It was my daily driver. Now I'm on my third Jeep, a '98 TJ and looking for a CJ5.
Hope this helped a little.