It is becoming forgotten technology - as is your coil and distributer - etc.
Again it shows how forgotten this is. A tyre fitter should have looked at your rim and thought - "hmm? - no safety hump - maybe this should have an inner tube?" they just don't know any more.
Don't buy them on E-bay or Amazon. those Fascist bully boys are killing small specialist businesses.
Oo but they are cheap i hear you say.
they are cheap because they sell cheap tat. If it is cheaper it isn't he Michelin tube. and they are just being flogged by someone who has no idea what it is for and will happily sell you a wrong tube.
Why would you not just contact the right people? Why would you not contact a specialist tyre dealer? They will sell you the righ thing at the right price. rather than some thing that doesnt cost as much because it isn't as good or is the wrong size?
Tell your local tyre dealer to contact Longstone Tyres, or any of the world wide Pirelli Collezione distributers off this web site
https://www.cinturato.net/ where you also get to watch a very cool advert where a lorry driver drinks a magnum of red wine while driving and smoking fags. they don't make adverts like that any more.
Or the Pirelli Collezione web site
https://www.pirelli.com/tyres/en-ww/car/collection
A failing with the classic car world is their obsetion with being cheap. A pre war car club i am involved in had some engine blocks made, and within their obsession to get them done cheap the blocks ended up being pourous. I have bought so many electrical components for classic cars over the years where the manufacturer has obsessed on the being cheap and the have let me down immeiately. and you spend hours trying to fix the car because it can't possibly be the condenser. I've just replaced that with a new one.
Dont be tight. Buy the right thing off the specialist who understands your car. You cannot, for one minute, think this is expensive
https://www.longstonetyres.co.uk/tyres/125-12/125-sr-12-cinturato.html