We can eliminate the 21st Tennessee as losing flags at Island No. 10. Their large silk Polk Corps flag is owned by Battleground Academy in Franklin, TN but is displayed at the Williamson County History Museum. Their Bragg pattern battle flag that replaced this is in private hands today and they would not have gotten that until probably May anyway.
There were three different portions of the Island No. 10 campaign - New Madrid, MO, and some flags were taken at the captured CS forts there; Island No. 10 itself, and some flags were taken there too; the CS surrender at Tiptonville, TN across the river and flags were also taken there.
Larry Daniel's fine book on this campaign makes mention of some of them but I would bet that most of the CS flags taken were never sent to the War Department
If you come across anything more for this campaign and CS flags please let us know.
Greg Biggs