Bjarney, Pyro is short for Pyrotenax, it is a brand of Mineral-Insulated, Metal-Sheathed (MIMS) cable. Lyle, Have you tried the site of Radio Spares Components? (RS Components) as they used to sell tools for Pyro work.
Bjarney, MIMS cable is invariably made from a Copper Sheath with a Chalk inner holding 2 or more wires in suspension. The wires themselves, having a 200 degree C+ rating. They are used in the Non-US Areas for providing circuits in Boiler-Rooms and other High Temperature areas. Biggest thing that anyone that works with MIMS, will tell you, is moisture!. Allow a wee bit of moisture into a MIMS cable and see the Insulation Resistance to drop like a stone!.