Try this place. They will have the parts on hand just bring your seals in and they will have them. I use them all the time. Also would take the piston and end cap of the cylinder with you for measuring. Very good people. They will also repair the whole cylinder for you. The even have chrome shafting and can make a new shaft for you. Check them out on the Web. Hope I have helped!
Yarbrough's Machine Shop CO Inc
514 North Fremont Avenue
Springfield MO 65802