Hi,

Update
I have called a company who told me to call another company who told me to call another company who told me to call the first company again.
I have not called them again yet, but will soon.

On of them was Wacker, http://www.wacker.com , they are quite specialized in silicones but they could not deliver this, at least the Swedish office
didnt know about a heat expanding silicone, but, they told me that it could in fact be an ordinary RTV2 silicone, that expands in heat just like any other material.

http://motoform.blogspot.se