Hi David
I bought some tyres from the club shop a couple of years ago, they are dated 2018 and still have 6mm of tread but not a lot of use recently. Michelins of course and the tyres they replaced still had plenty of tread but dated from the 1980s, I think Michelins use a hard rubber compound. As far as I know only Michelin and Blockley make metric tyres to fit Citroen rims.
Cheers Richard
Richard Larter