Nickel anit-seize paste... that's the ticket! I never knew it existed. Many thanks! (Buying some right now)I only use nickel anti-seize. Not easily found but once you have it, it lasts for awhile. If you are running exhaust at +2kF, you got some real issues. The stuff is good to 2.4kF/1.3kC.
I'm certain you can find solid copper nuts but as soft as copper is, I sure would not want to use them. Sounds like an ideal way to strip nuts in the future. I always thought that the copper plated were copper till I tested them with a magnet. I doubt if any factory uses solid copper. There are all copper plated. I always thought they were plated for rust/corrosion/seizing protection but it does not matter, I always use them.
The right stainless works with exhaust but typically people see stainless and just bolt it on. Then they find that they are all friction welded during disassembly. Mercedes used some Inconel studs/bolts/nuts on their older turbo diesels. That stuff was really expensive but I never had issues with seizing.