The UK is probably your best bet if you want new, just an example.
https://britishclassicspareparts.com...gc-ah-3000-bj8
Not cheap though. Where are you located? Perth brake parts is Aladdins cave of recon and nos stuff, maybe worth a try or somewhere local to you.
Rebuild kits are readily available may be easier to recon and old set.
*Edit* double check the thread sizes aswell I recall them being different between early and late types