Biographical Directory of American Congress a book I've used for Civil War research and other interests. Mine is 1774-=1971 & is mostly biographical but gives all Congressional Sessions and MOC Senate and House along with those replaced due to their loyalties in the Civil War. It is an inexpensive book (under $20) but excellent for the info it contains.

American Ballot Box in Mid-Nineteenth Century by Richard Fraklin Bensel. I have a hardcover bought in pre-internet (so: expensive) but I've seen it in softcover at an affordable price. It may sound a bit academic but do you really know how elections were conducted? And there is much on Missouri, my favorite locality.

Contested Elections in Congress 1834-1865, Govt. Publication, 38th Congress. Missouri had five contested elections in the US Congress in the Civil War. This book gives synopsis of contests that include these Missouri cases: (Bruce vs. Loan; Price vs. McClurg; Birch vs. King; Knox vs. Blair & my favorite: Lindsay vs. Scott.) Each had a publication of testimony but the Price and Birch cases were passed by the committee as they argued issues same as in Bruce vs. Loan. The Knox vs. Blair was of Course Frank Blair

Give these alook see and I am sure you will be pleased. Bob