What we now call the cavalry is represented in your display case... by the eagle-D (Dragoons) button. The US Cavalry did not come into existence until 1855, and then only two regiments were authorized to be formed, until more were added with the start of war in 1861. So it's not too surprising that nobody wearing eagle-C buttons seems to have gotten to the 1851-62 New Mexico fort you're hunting.
Great display of buttons and CW lead. Great job. The cone shaped bullet you mentioned...if you are referring to the top left bullet, that is a Ring Tail Sharps bullet, and a nice find.