I assume Reevolving won't be convinced by any of my suggestions, but here's giving it a shot, just in case some other wanderby happens to find this useful.
The best "deep freeze winter cardigans," as you put it, are the chunky lambswool, camelhair, or cashmere kind that Grammaton Cleric posted. LL Bean Signature probably has the cheapest one I've seen, though I've never worn or handled it. I think Club Monaco comes out with something similar every year as well, though their new design director, Aaron Levine, may have killed it (I don't know).
Better ones can be had through a number of Scottish makers, such as Hawick and William Lockie. Some traditional American clothiers, such as Ben Silver and O'Connells, will stock these. So does Kabbaz-Kelly. I assume the one at Peter Johnstons is also made by one of these manufacturers. I think Johnstons of Elgin and Pringle used to make chunky cardigans, but I don't know if they still do. Drake's sells a superlative one, but it's very expensive.
Oh, and Ovadia and Sons sells one. Unlike their other clothing, it's not as skinny in fit, but slim enough for a man under a 38R to wear. I have one and it's very warm. Chunky, made in Scotland, and constructed from lambswool.
The problem with the ones Reevolving posted is that they're not "deep freeze winter cardigans" - they're just cardigans. Some of those are made from a cotton blend as well, which of course means they're not warm. On the upside, you can layer plain cardigans under heavy outerwear, but they alone are not something you can wear outside.
Arguably, you should never wear just a cardigan in "deep freeze" weather, but if you had to, I would go with a chunky multi-ply cardigan made from cashmere, lambswool, or camelhair. FWIW, I only wear mine at home and use it to save on the heating bill.
Really, the person to answer this question is RJ, but he's unlikely to pop up here unless it becomes a true clusterf*ck of a thread. I hope my mistakes in this post have contributed to that possibility.
Edited by dieworkwear - 9/16/12 at 9:47pm