69 l78 distribution /prop/hold off valve orings

[camaro1]

Ive exhausted my search, I'm trying to find a source to obtain the orings/cup seals to rebuild all three valves in my j52 power brake set up, I know I can buy replacement valves but I would really like to rebuild them myself. Any one know of a source to buy oring/hardware kits(prop is easy) the other two not so easy (distribution and hold off valve on the frame rail under the driver floor)

Thanks Rich