You need at least to be on the prewar Matchy forum which is free, I'm not sure how you join - PrewarWDAJSM@AJSMatchless.groups.io
Or become a member of the Jampot Forum, which costs a small fee.
I'm sure you know these bikes are worth a few bob these days, and parts are keenly sought after, so it will cost you to obtain all the bits.
Fortunately lots of stuff is being remade these days, so its not like operating in a vacuum....
There was chit chat recently on replica exhausts, so those at least are obtainable in good quality.