There may not be a book to check out or read online - or many articles - about every agency.
These reference books - for use in the library - provide some information about most agencies on your list.
They are encyclopedias -- they provide general overviews and background (not current news) about federal agencies.
Use the index (back of the book) to see which pages discuss your agency.
In some cases, you'll find material under the agency's full name. Example: "Bureau of Alcohol, Tobacco, Firearms and Explosives".
In other cases, the acronym will work, instead. Example: "ATF".