www.bartiesworld.co.uk/postcards/ship_list_commercial.htm

This is a tabulation of ship/ferry postcards from many countries, many of which show paddlesteamers.
The largest quantity would be Bosphorus (Istanbul, Turkey).
Several have links to external sites.
Amongst the UK links there is one to PS John Benn (Greenwich ferry).

Regards,
Roderick B Smith
Rail News Victoria Editor