If I can call my local parts store and get 90% of the mechanical parts for my 78 Lebaron and even for my old 72 Coronet, We have a while before the K car parts are completely gone. There are still plenty of junkyards that have them for parts. Go to Car-Part.com and check for parts for an 81 aries. There are all sorts of body panels and other parts around, you just need to know where to look. Spend some time, call around and they are out there, they made hundreds of thousands of them. I'm not saying its not a good idea to stock up spare parts, that is always worth it.
As far as repairs go, anyone who is even slightly mechanically inclined can generally diagnose a problem by checking the codes using their key and doing a little research or question asking on the internet. Find an older mechanic and they will generally know what they're doing. I have factory shop manuals for everything I own and then some, they're sitting on the shelf collecting dust. A good mechanic can diagnose problems without it.