Hello,
The Tennessee State Library and Archives has a full run of Tennessee newspapers so if you know the dates and locations of the reunions of the 9th Cavalry Battalion you can find them that way.
For online subscription sites, besides newspapers.com, I also subscribe to Newpaperarchive.com and Genealogybank.com. Free historic newspapers can be found on the Library of Congress' web site Chronicling America. Try them all.
Greg Biggs