Peter, sun visors come up for sale regularly on eBay, that said I received an email from Wilkinson not long ago and he has reproduction sun visors, that were on special for $100 a set.
https://panterapartsusa.myshop...s/seats-and-interior
I think if you search here there are references to the correct style headliner material and sources for purchase.
For seat belts I used an aftermarket set, very similar to original design.