Of course, books and magazine articles on the battle. Depending on the details of the battle, could get down to the regimental level. My limited experience is that most do brigade and above.
Official Reports written by commanders (regimental, brigade, etc). Check both Union and Confederate sides. If the unit was bested by a Union unit, am sure the Yankee Commander would write about it.
Not sure if books were written by members of this unit, but my recollection is that in Art Bergeron's book on Louisiana units, there was a bibliography after each unit.