On the commuter forum you might find some people that have changed tires in subfreezing weather, you might find some good comments there. I do not ride in sub-freezing weather, my comments are not based on biking experience, they are only guesses. If it was me, I would carry two pumps, those two are described below.

You have probably read on this forum that a favorite for touring is the Topeak Road Morph G, however that has many plastic parts. A pump of similar design is the Lezyne Micro Floor Drive which comes with or without plastic gauge. There is a plastic hose and a plastic part at the end of the hose, but most other critical parts are metal. Comes in a high volume or high pressure version, the link below is for the high pressure type without gauge. This pump has a part that threads onto your valve stem instead of clamping on, thus it would be quite inconvenient to use with insulated gloves and likely impossible to use with mittens.
http://www.wiggle.co.uk/lezyne-micro...without-gauge/

Some of the parts on older Zefal HPX pumps were plastic, but most of the important parts were metal. These pumps have been a favorite for decades.
http://www.zefal.com/en/traditional-...x-classic.html

You will want to take care to avoid getting moisture into your pump where it can accumulate and freeze. If you get a pump that will fit in your panniers, you may want to consider carrying it there instead of outside where freezing rain and sleet could make it inoperable. If you do accumulate some ice in the pump, you may need to thaw it out overnight in your sleeping bag and remove as much moisture as possible in the morning before it re-freezes.