If you are looking only for Spencer carbine ammunition, you are going to severely restrict your search.

I have seen numerous accounts where the members of the 2nd Missouri Light Artillery were issued a variety of arms. There is mention of some of the men possessing Sharps and Smith carbines. Some of the men were only issued Colt army revolvers.

The 12th Missouri Cavalry was equipped primarily with Gallagher carbines. I think they may have had only a company or two equipped with Spencers, if that.

An end of year quarterly ordnance report for 1864 showed the 16th Kansas Cavalry as being equipped with 70 Burnside carbines, 95 Starr carbines, 54 Smith carbines and 310 Gallagher carbines. I would assume this is the type firearms they probably still carried in 1865.

Good luck on your research!

Gil