To answer your question you actually had, I do not know of any surviving flags or photographs of them for the 3rd or 6th LA Cavalry, nor the 28th LA Infantry. However, the man that would know would be Ken Legendre. He is considered by many to be the expert on Louisiana flags from the Civil War. You can contact him via a recent post on the "Flags in the Civil War Message Board". Simply go to the top left of the main page of the Louisiana in the Civil War Message Board and click on "message boards". You will see an option for "Special Interests" and under that click "Flags." Ken recently left posted on that board so click on the response with his comment and ask him about the aforementioned flags. Good luck in that endeavor.