Don't ya just take it apart, and cut the leather off of an old show and wedge it between the piston flanges? Soak the leather in old motor oil after it's on.
I see that tire pump rebuild kits are available from Lang’s,
at www.modeltford.com you will have to check if the diameter
of the replacement parts will work for you.
Bratton’s sells the hose and some clamps, but not the leather cup. I may end up having to find a shoe and do some trial and error work. Maybe Goodwill will have some cheap shoes I can buy and cut up. I was hoping for an easier solution.