I have been researching this subject off and on for a while. It seems that the use of US eagle buttons by the Richmond Depot was pretty common. I don't know about the other depots. The source of these buttons is somewhat of a mystery. One source was likely the salvage efforts of the CS quartermaster corps. On every battlefield that remained in CS hands the quartermaster would send people to collect all useable items. This would also include cast off or unissued/captured US uniforms. These would have been one source of buttons especially for the Richmond depot since they were close to the major battlefields. I also remember seeing an inventory list of buttons imported into the CS states around mid war. There were thousands of eagle buttons listed but I can't seem to find the source of the document. It was way too many for them to have been CS staff officers buttons. If one looks at the pictures of dead Confederate soldiers from the Lib. of Congress, most of the coats where the type buttons can be distinguishd have eagle buttons(especially around Petersburg). There is an example of one of these pictures on