Try contacting Power Brake Sales 1517 McCormack Ave, Sacramento, CA 95811
Talk to either Kathy or Sandra... both have years of experience.. I'm guessing they will ask you for the tag information off your existing unit and can either offer you a remanufactured unit.... or can do yours.......
their mainstay business is truck and air brake applications .... they do Air Compressors, offer valves, all kinds of current and service parts for older units...
Hope this helps...
Retired Business Owner, Re-manufacturing HD Clutches, Brake Shoes, Air Compressors, Sales & Installation of PacBrake and other Industrial Friction