There is an image of the 8th Cav regimental flag on the back of David E. Casto's book on the regiment in Arkansas during the last year of the war. The image is attributed to the Missouri State Museum in Jefferson City, so I imagine that is where it is at the present time. I would address my questions to them.

The book I reference above is Arkansas Late in the Civil War: The 8th Missouri Volunteer Cavalry, April 1864-July 1865. It is well researched and written. I recommend it.