Where are the latest drivers for the Intel HD Graphics 4000? Strangely enough, I haven't been able to find any official website or webpage that hosts the official Intel HD Graphics 4000 latest drivers for OS X (10.9, to be specific).

Where are the drivers hiding?
The drivers for Intel GPU HD4000 are modified by apple and the revisions are delivered to you bundled in software updates.

If you want a access to specific driver open the installation package from 10.9 with specific tools for that and get it from there.