Especially with something like the Grand National, the only thing keeping any GN-specific parts available at this age is enthusiast demand. It's predictable/understandable that the majority of support for a car like that would move to aftermarket if not niche specialist - I'm heavy in those circles with 70's-80's Mercedes diesels. However, over just the last 3-5 years the number of different parts that are shifting to drastically worse quality or just being discontinued altogether is accelerating. But when situations like above^ present themselves with cars that are nearly-new and produced in higher numbers than your C6 or GN ever were to begin with, it undermines any argument that older stuff is fundamentally "harder to get parts for".