There is no organized dub repository AFAIK. The newsgroups have most of the official GOUT dubs, and then there's Portuguese, Czech, and incomplete Japanese dubs (maybe others?) floating around somewhat aimlessly. And then there's the matter of improved dubs, such as the improved German dub.
IMO, at this point, more dubs will do more to help Star Wars than more subtitles. In particular, the Hindi dub.
What are your improvements? I'm interested to hear about it!