check this link with railtourism. org. they arrange charters for upto 170 passengers - check this link - www.railtourismindia.com/cgi-bin/dev1.dll/irctc/booking/charter.jsp
These are run by irctc people and phone nos are also given. contact them and you can get direct precise details. thanks.
the alternate link is - www.railtourismindia.com/Trains/HillCharters/hillTravelPlanner.html
and opt for charter booking