Under what conditions? Oxidising atmosphere? I doubt you can use the carbon for long at 1000°C. The bigger problem is the resin/binder anyway.

Why not use a ceramic, or simple graphite? Metals should work, too. Unless you look at exotic materials like reinforced carbon-carbon these are the only options that make sense.
https://en.wikipedia.org/wiki/Reinforced_carbon%E2%80%93carbon

That's graphite with embedded carbon fibers. Expensive, that material might cost more than the oven. Just use the normal stuff I mentioned above.