Timely and current information regarding RHIOs in the United States is available at NHIN Watch, http://nhinwatch.com/performSearch.cms?channelId=1
The Office of the National Coordinator for Health Information Technology (ONCHIT) offers a listserv mail list which announces what ONCHIT is doing to advance RHIO development.
It can be found at: https://list.nih.gov/archives/health-it.html