Where can I find one ready for use? Or for that matter, a good collection of "standard" data structures, if you know of any?
A quick check o' the Interwebs turned up a ready-to-use implementation from Kevin Lindsey (scroll down to Red-Black Trees):
Unfortunately I don't know of a site that has a repository of ready made complex data structures.
I'm guessing they're a tad rare since people rarely use JavaScript for the kind of heavy lifting that would necessitate those kinds of complex structures...but I could be wrong.