Many guides to sources are gathered in this LCSH:

United States -- History -- Civil War -- 1861-1865 -- Sources

Henry Putney Beers, The Confederacy: a guide ot the archives of the Government of the Confederate States of America (NB, this is a bibliography, not a sourcebook. Many of these sources may not be at Vassar; try ILL or hathitrust.org

Ira Berlin, Free at Last: a documentary history of slavery, freedom and the Civil War

Garold Cole, Civil War Eyewitnesses

R.U. Johnson & C.C. Clough Buel, Battles and Leaders of the Civil War: being for the most part contributions by Union and Confederate officers

Brooks D. Simpson & Stephen W. Sears, The Civil War: told by those who lived it

Look up any single title newspaper or magazine in the yellow "Journals" tab at center of library website to confirm Vassar's holdings.

Limit the date-range to explore what Civil War journalism is included in the larger, mulit-title database collections.

Below are links to the results of an "author search" for the listed individuals. I chose to link to these results so you can see print and digital holdings in all their various editions and publications.  Even Lincoln's is only 3 pages of results and quick to scan through to find what you need.