[pmulcahy11b]

Here's a possibility: Local progress. Except for the November Nuclear Strikes, the nukes and chemical warfare came in dribs and drabs. Some places that already have a decent technological base, but are otherwise intact (even if for only a while) might develop stuff that saw only local use or small-scale production and issue to overseas troops or nationwide. Offhand, I can only think of a few spots, mostly in the US, but:

Groom Lake (the so-called "Area 51"), Edwards AFB (probably would have been hit early, but it's a huge base), various places in Silicon Valley, and Crane Weapons Center. If you go by some Challenge magazine articles, the Lima, Ohio M-1 Abrams plant is relatively undamaged. Maybe throw in some deep-secret, underground development labs (could go for lots of countries), isolated gunsmiths, and prototypes that some government facility took to fruition, but couldn't make many of. Old experimental projects could also have been dusted off, maybe updated a bit, and put into production early in the war. Wartime expedients would also have happened; I once played a character in a late-war draft that was told to show up with his own weapons, ammunition, and equipment if possible (luckily, he was an outdoor enthusiast and a gun collector).