Rear brake master cylinder help

Hi everyone, I’m new here. I’ve just bought a 1978 XS that needs some work including an overhaul of the rear master cylinder. Can anyone put me on to somewhere i can get hold of a refurb kit including new piston?
I’m in the UK and I’m really struggling to find 1 here so any help from worldwide much appreciated.
Thank you

To be honest I do not think they make one with a piston...........I had a 78 and I just bought a brembo rear master and fabbed up a bracket.......... doing a DOHC bike now and am using a rear disc on it and a brembo master also..........they can be found for 100 bucks or so just have to search it out.

Good luck!

Thanks for the reply. I think I’m going to look at fitting a ‘generic’ unit, something like below

Yeah, the kits are essentially unavailable now. Someone said there was recently one on Ebay for $400 but I didn't bother looking.