you might try classic spares.
www.classic-parts.co.uk they advertise brake and clutch parts, located kenton, Devon.
past parts ltd.
[email protected]Have you checked local newstands for Classic and Vintage Commercials or Heritage Commercials they may have useful leads.
Jim Carter Also sells Hydrovacs
www.oldchevytrucks.com but he requires a core or core charge will apply.