In my local shoppping center there is a lady who decorates cakes (known as the “cake lady”) who drives a 1980 Pontiac Bonneville with nearly 300,000 miles on it. Her husband maintains it well, but does not go to extraordinary lengths to do so. Every weekend they take it out on a long enough trip to thoroughly warm it up and blow out the cobwebs.
So I think you have many years of happy motoring ahead of you. Don’t worry about parts in this case. Those GM cars were cookie cutter badge-engineered copies of each other. And wrecking yards will have enough body and trim parts.