Even in SoCal, where cars last a long time, 25-30 year old vehicles become scarce in the local junk yards. Particularly the dismantlers. The dismantlers get their inventory through contracts with insurance companies. At about 10 years, the vehicles are not likely to be insured for comprehensive and collision because they have depreciated enough that they aren't financed, which requires the coverage. So the older cars aren't on the contracts, and don't go to dismantlers.
As they wear out and get wrecked, or suffer a mechanical malfunction that is cost-prohibitive to repair, they end up in the pick-a-parts. My observation has been that in the area of the yard I frequent that contains about 300 similar vehicles (domestic SUV) there is now only one or two 1st gen S/T, if any, and they are in pretty sad condition. There are still lots of Astro/Safari, and I go to those for engine parts such as brackets and pullies, etc.
"The junkyard" isn't as reliable or practical a resource as it was a few years back. These cars are becoming scarce. Not to mention "a late '80s Grand Am or Sunbird. A Skylark" wasn't very prolific or popular when they were new. Gonna' be really tough to find 25-30 years later.
But not a bad suggestion. I need to find one of these ECM's to strip the connectors out of. So I still look for the Quad-4's. Haven't seen one for 15 years.