There are hundreds if not thousands of different mechanical counters avalable, you just need to figure out how to mount it so some part of the handle or ram hits it every time you pull the handle... mechanical would be my choice so you dont have to worry about batteries....
here is one example....
http://www.amazon.com/Tally-Number-M...anical+counter
im sure a little searching could come up with a 6 digit version...