One of the first things you might consider when looking for primary sources for your research is what kinds of things are common to the time. What types of communication, documentation and material culture were produced in the mid-nineteenth century and by the people/events you are interested in? A little background knowledge and a little imagination can start you off on the path by using specific search systems and keywords.
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Historical documents and other primary sources including personal writings of women of the 1700s-1900s from around the U.S., drawn from the collections of the American Antiquarian Society. The letters and diaries reveal, in each woman’s own handwriting, the details of the authors’ daily lives, their activities and concerns, and their attitudes towards the people and world around them.
Contains the full text of early African American poems, from the first recorded poem by an African American (Lucy Terry's 'Bars Fights', c.1746) to the major poets of the nineteenth century, including Paul Laurence Dunbar and Frances Ellen Watkins Harper.
Historical documents and other primary sources focusing on the work of African Americans to abolish slavery in the United States prior to and during the Civil War (1830-1865).
Historical non-fiction writings by notable Black American leaders—teachers, artists, politicians, religious leaders, athletes, war veterans, entertainers, and other figures—covering 250 years of history.
Photography was a revolutionary new medium in the Civil War era. Understanding the history of the medium and types of photography available can give context on their purpose, who it was available to, and more.
Maps and Mapmakers of the Civil War by 
The Routledge Atlas of African American History by Books are an excellent place to find reprints and transcriptions of original documents and images. You can use Keywords to search for books, or the Subject Heading for primary sources "Sources" by changing the drop down from "Any Field" to "Subjects."
The mid-1800s were a time of great change for communication in the United States. The advacnes in transportation and the telegraph dramatically increased the speed information traveled. Furthermore, the federal government subsidized the distribution of newspapers through the U.S. Postal System. Communication with the public was vital to the war effort on both sides, and modern journalism as the profession we think of today was formed as a part of that. However, newspapers were still quite different than today and were often heavily partisan (backed by a political party or group).
Understanding how newspapers functioned during and after the Civil War is vital to place them (and the information they give) in the context of the times. See the following for brief overviews.
Fanatics and Fire-Eaters by Historical American periodicals (e.g. news, magazines, & journals) published between 1684 and 1912 in five series, all searchable through one link.
A historical newspaper archive including images of both full pages and clipped articles for hundreds of 1800s U.S. newspapers. For each issue, the newspaper is captured from cover-to-cover, providing access to every article, advertisement, and illustration.
Historical periodicals (e.g. news, magazines, and journals). Titles include Benjamin Franklin's General Magazine and America's first scientific journal, Medical Repository; magazines such as Vanity Fair and Ladies' Home; and more.
While early photographic processes such as the Daguerreotype existed during the Civil War, it was not until the late 1800s that photographs were printed in newspapers, and not until the early 1900s that it became a regular practice. However, with the invention of the Lithograph, illustrations were common in the news. Political Cartoons were also a common way of influencing readers.