The latest builds of x264 are still hosted on
http://mirror01.x264.nl
If that one breaks down, it's mirrored at
http://x264.x265.net (use the links on the page for mirror02, the page is edited so that when clicking on mirror02 links you access this domain)
Future builds may be hosted on other domains, but you guys will be informed before that happens so no need to worry about it.
(for some reason the apache server crashed a few hours ago and the watchdog service didn't catch it, that's why the mirrors above were down if you checked them, should work fine now)