Bruce Nichols "Guerrilla Warfare in Civil War Missouri 1862 is a good place to start he has a number of pages on the 8th MSM . I am sure his 1863 and upcoming 1864 editions would have some information has well. Cornnel University has online quite a few if not all the "Ors" or Orignial Records of both the Union and CSA forces. That doesn't mean that they will have all the reports of the 8th MSM has some may of gotten lost over the years but maybe you will get lucky. The Missouri State Historical society might have something and if you have time to look up old Mo newspapers that might work. However to save time I would order the above book at Amazon or Barnes and Noble.

Leonard