Good luck.
You are looking for what the US military (and the people who build stuff for them) calls "rugged conduction cooled components". Not only only that, but you want something on the most demanding end of that bell curve.
Rugged conduction cooled means active and extreme measures are taken to bleed off heat, as described here (linking does not equal endorsement, I've never heard of these guys but the white paper seems good), either because air cooling with passive measures like heat dissipation via design or active measures like fan cooling is insufficient, because air cooling introduces a new complication like dust, or in extremely small form factors where you simply don't have enough room for the amount of air you'd need to realistically cool the components.
Computer gamers do a similiar thing. High end gaming machines can get extremely hot, and you can literally cook your desktop playing computer games. Running tubing through your machine and pumping cooled water will allow you to shoot all the virtual Nazis you want without worrying about your fans, and is a lot quieter besides.
Generally speaking, it's easier to warm the computer than to cool it, at least at the level you're describing. A heating element in or on the PC is a trivial matter compared to the difficulty involved in bleeding heat.
If you're looking for a PC that can handle -40°C up to +80°C, the only guys I can think of who make a COTS unit is probably going to be GE. Assuming you have a government level budget for the project, of course.
I hope this helps.