Unfortunately the UK still does not allow many ebooks from Victoriana online. Thomas Frost’s 1874 book ‘Old Showmen and the Old London Fairs’ is one such book. However it is available in the USA at the archive.org website. Frost’s volume is a good starting point for researching Menagerists and other showmen through the 19th century. It makes a quick and easy interface for researchers and others interested in the period. Be warned that it has sometimes relied heavily on perpetual myths and other unqualified reports for its information. At this time it is a free online read.
The link is: Thomas Frost