thanks for your mail, there is a book called the "The Coins of the Sikhs" by Hans Herrli, it is the most comprehensive book on Sikh coins to date and a must for all collectors of Sikh coins. Gurprit Ji is a member of the Coin Network and runs a group about Sikh Coins and here is the link for this group :-
This group is dedicated to academic and intellectual interaction on Sikh Numismatics, including the numismatics of Cis-Sutlej States such as Nabha, Patiala, Kaithal, Malerkotla etc. Within the groups PHOTO section there are something in the region of 700 scans of Sikh coins from various mints. These have been organised by Mint towns, Marks and historical significance. Combined with messages which are titled with the same name as the photo album.
I am also hoping to add some information in the months to come on this group about the Sikh empire, coins and history to assist members who may not be aware of this. In the meantime should you need more information please just feel free to mail me.
Please let me know were you are based so I can try and assist you in purchasing the Hans Herrli's book which, was actualy printed in Delhi, India.