The rear diaphragm rubber has fragmented like a busted balloon!

I understand a Girling Supervac 100 is a bolt-in replacement, but googling and an eBay search has turned up nothing. Is there a better way of finding one?

Trying to make it for a local Jag club event in 9 days, after working on the car for nearly two years.

Sorry to drop in to this forum with a "first post of desperation". I'll eventually get around to properly introducing myself and my interesting project car. Thanks for any help.