Ok...a little fun with figures...
10 foot diameter circle at 500 feet.
Let's say we want to light that to 5 fc (not very bright.
However, that means we need 1,250,000 candela output. I have measured two 1,000,000 candela (candlepower) spotlights at 100,000 and 65,000 cd (the two I have in my sig--the Vector is the brighter).
BUT since you only want to light the 10-foot circle (which is 250,000/((10/2)^2*pi) steradians, then you would divide the 1,250,000 candela by that answer and end up with 393 lumens IF it is all focused on the 10-foot circle.
We are talking some killer optics and at least a 20W lamp.
I don't think the UKE Light Cannon is tight enough to meet your criteria. The UKE SL6 falls way short at about 13,000 cd (measured).
I do NOT believe any of the candela ratings in this thread--except perhaps the UltraStinger IF and only IF it is focused down to a pinprick. The SL-6 is a fairly tight beam and is an 8W lamp for about 160 lumens (though in a conversation with UKE they mentioned 200).
Perhaps the best resource for looking at this stuff is Brock's flashlight page
http://www.uwgb.edu/nevermab/flash.htm
The only thing that comes close is the N62 lamp assembly from SureFire...but that only runs 20 minutes on 4 123-cells.
I don't think you'll find any of the Litebox types of lights that far-throwing, but you might look at the Streamlight ones. The Sealed Lead Acid battery should be good in the cold, too, but it's not light weight.
Anyway, I don't think you'll find what you need.
Oh, and see if you can use rechargeables in the Light Cannon, 'cause at -20, alkalines are toast.
Cheers,
Richard