Source: http://query.nytimes.com/mem/archive-free/pdf?_r=1&res=9806E3DD143AE533A25750C2A9619C94609ED7CF
Text (transcribed):
New York Times
July 23, 1891
New Orleans, July 22. - The daughter of the late Confederate General Harry T Hays, turned over to-day to Col. A.S. Graham, an officer of the Grand Army of the Republic, the Battle Flag of the Fifty-seventh Ohio Regiment, which her mother desired should be returned to that regiment. Col. Graham will take the flag with him to the National Encampment at Detroit next month, and return it to such survivors of the regiment as may be found, or some typical Ohioan, possibly Comrade Foraker.
The flag is certified by Capt. A. L. Guzman of the Eight Louisiana Infantry of Hays’s Brigade to have been captured by Private Wittes of Company I from the Ohio Color bearer, in the charge upon Cemetery Hill, at the Battle of Gettysburg, on the second day. It was turned over by Col. Guzman to Gen. Hays, and has reposed in the keeping of the family until now.
Also, found a second reference to the flag. This web site is 'modern' but references a encampment of the SUV in 1890.
Source: http://www.suvcw.org/banner_nl/2008BannerSpring.pdf
Text (Page 7): A letter, received from the wife of Confederate Gen. H.T. Hays, offered to return the flag of a Union regiment, captured by the 8th Louisiana at Gettysburg. The Encampment extended its thanks.