Start with books about the publisher, author biographies, author-publisher correspondence.
Do a subject search in OskiCat/Melvyl using the subject headings:
Best sellers
Best sellers--Bibliography
Best sellers--Great Britain
Best sellers--Great Britain--Bibliography
Best sellers--Great Britain--History
Best sellers--United States
Best sellers--United States--Bibliography
Best sellers--United States--History
Books and reading--Name of Country--History—Century
Try more specialized resources:
Altick, Richard Daniel. The English Common Reader: A Social History of the Mass Reading Public, 1800-1900. Chicago, University of Chicago Press, 1957. Main Stack Z1003.A57
Altick, Richard D.: "Nineteenth-Century English Best-Sellers: A Further List." Studies in Bibliography: papers of the Bibliographical Society of the University of Virginia (Charlottesville, VA) , XXII, 197-206. (1969)
Altick, Richard D.: "Nineteenth-Century Best-Sellers: A Third List." Studies in Bibliography: papers of the Bibliographical Society of the University of Virginia (Charlottesville, VA) (39) 235-41. (1986)
Altick, Richard D. “Publishing,” in Herbert F. Tucker, ed., A Companion to Victorian Literature & Culture. Malden, Mass. : Blackwell Publishers, 1999. Main Stack PR461.C597 1999
Bassett, Troy J. and Christina M. Walter. “Booksellers and Bestsellers: British Book Sales as Documented by The Bookman 1891-1906.” Book History (4) 205-36 (2001).
Bloom, Clive. Bestsellers: Popular Fiction since 1900. Houndmills, Basingstoke, Hampshire; New York: Palgrave Macmillan, 2008. 2nd ed. Main Stack PR888.P68.B58 2008
The Bookman (London, not to be confused with the U.S. publication of the same name). From its inception in 1891 until after the turn of the 20th Century, The Bookman included lists of bestsellers. Not all these lists have figures of sales but, at the least, these lists give an idea of popularity. Hathi Trust has online for 1891-1922.
Bowker Annual of Library and Book Trade Information. 1961- Doe Reference, Main and NRLF Z1007.A513
Eliot, Simon. "The Business of Victorian Publishing," in Deirdre David, ed., The Cambridge Companion to the Victorian Novel . Main Stack PR871.C17 2001
Eliot, Simon. "From Few and Expensive to Many and Cheap: The British Book Market 1800-1890," in Simon Eliot and Jonathan Rose, eds., A Companion to the History of the Book. Malden, MA : Blackwell Pub., 2007. Main Stack Z4.C73 2007
Flower, Desmond. A Century of Best Sellers, 1830-1930. London: National Book Council, 1934. Main Z2014.F4.F6
Hart, James D. The Popular Book; a History of America's Literary Taste. New York: Oxford UP, 1950. Main Stack Z1003.H33
Hinckley, Karen. American Best Sellers: a Reader's Guide to Popular Fiction. Bloomington : Indiana University Press, c1989. Main Stack PS374.B45.H56 1989
Justice, Keith L. Bestseller Index: All Books, by Author, on the Lists of Publishers Weekly and the New York Times through 1990. Jefferson, N.C.: McFarland & Co., 1998. Main Stack Z1033.B3.J87 1998
Keeran, Peggy and Jennifer Bowers. Literary Research and the British Romantic Era: Strategies and Sources. Lanham, Md.: Scarecrow Press, 2005. Useful for anyone researching the Romantic period, especially Chapter 11, which looks at the process of finding information about print runs and sales. Main Stack PR457.K44 2005
Korda, Michael. Making the List: a Cultural History of the American Bestseller, 1900-1999 as Seen through the Annual Bestseller Lists of Publishers Weekly. New York: Barnes & Noble, 2001. Main and NRLF Z1033.B3.K67 2001
McAleer, Joseph. Popular Reading and Publishing in Britain, 1914-1950. Oxford : Clarendon Press ; New York : Oxford University Press, 1992. Main Stack Z1003.5.G7.M39 1992
Mott, Frank Luther. Golden Multitudes; The Story of Best Sellers in the United States. New York: Macmillan, 1947. Main and Moffitt Z1033.B3 M6
St. Clair, William. The Reading Nation in the Romantic Period. Cambridge, U.K. ; New York : Cambridge University Press, 2004. Ground breaking study reading and books. Though the focus is on the Romantic period, St. Clair ranges across four centuries of printed books and their readers. Of chief interest to English 200 are the appendices, 170 pages of figures on markets, book production, prices, and print runs. Essential for works published during the Romantic period; extremely helpful for others. Appendix 12 covers Shakespeare with prices and sometimes print runs. Main Stack Z1003.S77 2004
Sutherland, John. Reading the Decades: Fifty Years of the Nation's Bestselling Books. London : BBC, 2002. Main Stack Z1003.5.G7.S88 2002
Wright, Lyle H. “A Statistical Survey of American Fiction, 1774-1850.” Huntington Library Quarterly (2) 309-18 (1939). Article looks at all aspects of fiction and included a list of bestsellers based on the number of editions published.
Webb, R. K. “The Victorian Reading Public.” Higher Education Quarterly, 12 (1957): 24-44.
20th-Century American Bestsellers
Bestseller Lists 1990-1995 List developed and maintained by Cader Books and People Magazine; they appear to compile the list from information supplied by Publisher's Weekly.