According to the Girling catalog, that particular wheel cylinder is fitted to the following cars

[Linked Image]

so maybe one of those car clubs would have a source for the parts.

Otherwise, can you just make a set of new parts?

I always leave mine in gear when parked anyway, just in case the handbrake fails, or the passenger knocks the flyoff handle...

Dave
Blue 4/4 1969, Green +4 1953, (different) Green +8 1977