First, you did not make clear from your research if Thomas D. Day was a Union or a Confederate "commissioner." I conclude that Thomas D. Day was a Union officer for several reasons. In May 1863 all of the Mississippi River in Mississippi was under Union control except for Vicksburg. That city was still under Confederate control until Vicksburg and it's remaining Confederate garrison surrendered to besieging Union troops on 4 July 1863. This tells me that Natchez, some miles south of Vicksburg, was under Union control in May 1863, and a Union officer could have access to its newspaper. Because of that situation, I conclude that a Confederate officer could only post a notice in the Natchez newspaper during May 1863 with great difficulty, despite the humanitarian appeal of his notice. I could find nothing about a Confederate officer of Missouri named Thomas D. Day or anything close in several published lists of southern Missouri officers in either the Missouri State Guard or the Confederate Army. Officers of either side who were ordered to work on a commission, usually performed those special duties away from their normal assigned unit. What was Day's normally assigned unit, if known?
Second, there were several Missouri military commissions. Civil War commissions and commissioners could be of either side, their members could be military or civilian, and such commissions performed varied duties, sometimes of a humanitarian nature. I assume the newspaper notice clearly stated "Mil'y Commissioner of Mo," and not Mil'y "Commissariat" or "Commissary" of Mo." Is that correct?