Exchange Rate Postcards
I am a collector, living in Istanbul, interested in collecting "money postcards" showing Ottoman Empire coinage against other nation's currencies and exchange rates. The postcard above is printed and issued by "H.S.M.". In this series there are various patterns and designs in English, French and German. I have also seen other countries money cards showing their gold coinage parities with others, such as a Spanish money card showing exchange rates against British coinage, USA gold coin etc. all printed by H.S.M.
Can anyone suggest a source where I can find out about how many types of these exchange rate postcards were published, in which years they were printed, their historical development, how many publishers were there and if any of their catalogues or archives still exist?