The simple truth is that there isn't just one repository for ux's and ui's, and probably never will be.
This conversation has been going on for four years, and no-one can agree how it should be organised, who should be in control of it or whatever. The reality is that many have tried and failed, because everyone wants different things, and the licences prohibit it.
So put your ux wherever you like, and as long as it's on the extensions forum, people will see it.
I have also created a site for this purpose (around the 2.x/3.x mark) and was told that to hold off by Sencha (ExtJS at the time) as they where building one... which never saw the light of day, and to be honest it's a violation of the licence to host a ux site anyway (another issue that was never resolved) as ux's are quite often variants of licenced code (or include it directly), hense why many of us built our own sites.
GitHub is the official sanctioned UX repository. (as I've been told be Sencha people), but people have ux's in google, codeplex, private svn, public svn.
The problem isn't the lack of repositories, it's the lack of an interface to find them, and the fact that there are multiple naming standards, and multiple naming and versioning standards (just like every other community out there) and that's OK, we are all different.. senchaforge.org was about to be launched last year and I was told to holdoff on that which is exactly what you are talking about. Abe gave me a licence to build senchaworld.com and senchaforge.org but it was Sencha that became the bottleneck as they kept telling me they where going to do it.
There is around seven attempts still online that are hosting ux's. All of them are valid. People used to post their extension on the wiki, and that worked really well, but once version 3 came out, people got lazy and stopped taking 20 seconds to add their extension. Now we have an extensions forum, which works ok, but also has it's limits (depending on your oppinion).