Last Updated: December 19th, 2012
If you're looking for the Android 4.2.1 update to the Nexus 4 that started rolling out this morning (it's a very minor patch, at only 1.1MB), you can find it, straight from Google's servers, at this link.
The update, JOP40D, so far has one known fix: the missing month of December in the People app (Contacts.apk). Presumably it fixes other things, too - Google probably wouldn't release a patch just for a single bug, but we haven't figured out what else this patch may address just yet.
Last Updated: December 17th, 2012
Yeah, we know, Google goofed the Nexus 4 launch. It's a bummer. But if you didn't manage to get your order in, you can now obsessively check availability in your respective country using the Play Store Availability Checker. The site offers two view options: the whole Nexus device list for your respective country (link), or a list for a single device in all Play Store countries (link).