What machine do you have?
The Independence reportedly runs the TEG at about 200°C on the hot side, and a few high temperature modules are spec'd to 230°C (pretty close to 200°). This
discussion of TEG modules may be helpful.
You might take a look at
this site, which advertises "Thermal Interface Materials," which include graphite sheets a.k.a. "Graphite Thermal Interface Foil." According to them, "Graphite foil TIM is the only TIM able to survive temperatures above 250°C (482°F), so it is an essential choice for use on Thermoelectric Generators TEGs." Good Luck!