Links galore, Nick as usual have put up the new episodes on their site.
[caption id="attachment_8304" align="aligncenter" width="600"] Korra is ready for battle.[/caption]
http://www.nick.com/videos/clip/legend-of-korra-123-full-episode.html
http://www.nick.com/videos/clip/legend-of-korra-124-full-episode.html
http://www.nick.com/videos/clip/legend-of-korra-125-full-episode-m1a2t3t4.html
http://www.nick.com/videos/clip/legend-of-korra-126-full-episode-k4y3l2e1.html
They are region locked for anyone outside of america, but by using a program like Tunnelbear you can watch them.
I assume that during the week Nick will take down the last two episodes ahead of the TV airing and then put them back up, which may explain the odd links for those two.