Don, from what I have read, no, there are no IOS's that can be used on a platform to act as a RA Daemon, however, there is support for IPv6 DHCP IOS that can be used , which is the equivalent of an Router Advertizement Daemon.
Simply do a "search by feature" and look for IPv6 DHCP feature to list IOS and platforms that supports this feature. [edit] from there you can choose the platform for your test lab.
http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp
HTH
Jorge
Jorge Rodriguez