I did a little research on this on the garage journal.
I had a bad O-ring in one of the pump pistons in my chinese "Torin - Big Red" floor jack. I found out that it is a garden variety, but METRIC sized o-ring. I sourced the replacement at my local auto parts store taking the damaged on in for comparison.
If you are looking for a ram seal (I've never had one apart, so I don't know what they would look like), I would take it off and go to a hydraulics specialty shop. Most cities of any size will have one, since hydraulic rams are on everything.
They can probably match it up for a modest price.