Links - 19th century publishing and bookselling, etc
Sites including Thomas Richardson & Son publications
Revolution and Romanticism - a streetprint site - "from street ballads through chapbooks and tracts to valentines". Includes images of a ballad sheet published in 1836 by Thomas Richardson, Derby.
Chapbooks - from www.booksandwriters.co.uk. List includes Thomas Richardson publications.
The Hockcliffe Project - Hockliffe Collection of early British children's books from the Polhill Library, University of Bedfordshire. Includes images of T. Richardson publications
KidPrint: A Collection of Children's Literature - a streetprint site - "a repository of popular British children's literature from the eighteenth and nineteenth centuries."
I found the following databases and indexes particularly useful:
The British Book Trade Index - an index of the names and brief biographical details and trade details of people who worked in the book trade in England and Wales and who were trading by 1851. Searchable index.