According to this article on seibertron.com, the earlier figures in the United range are getting a re-release in April.

Early April:

Cybertronian Bumblebee
Cybertronian Cliffjumper
Straxus
Bumblebee
Drift

Late April:

Cybertronian Soundwave
Cybertronian Optimus Prime
Cybertronian Megatron
Optimus Prime
Megatron
This hopefully will mean that they will continue down the line and re-release the rest of the guys like Jazz and Tracks.