On the Exchange Team Blog, the Exchange product team posted two updates regarding Exchange 2007 SP3 RU3.
Yesterday, they announced that the re-release was coming soon. Additional information about the status of the Exchange 2010 SP1 RU3 can be found there as well.
Today, they announced that it has been re-released and that a new KB article regarding the update is now available here. The direct link to the download is here.