Q: I am looking for recommendations for fasteners capable of operating under load at 2000C, in a mild vacuum environment. The material can be conductive or insulating just along as it does not react with carbon.
A: For temperatures as high as 2000C, Zirconia ceramic fasteners would be your only option. Zirconia is usable to 2100C. This material will also be non-reactive. Otherwise you would have to have no oxygen present in your atmosphere. If that is the case you may consider tantalum metal fasteners. They are non-reactive but can only be used in an oxygen-free vacuum a those temperatures.