That's a beautiful car.
I'm assuming there may be a American collector car owners group near you... ?
Contact them for suggestions of which parts or service suppliers to use, or not use.
Some US parts vendors may not ship overseas, which would be extra expensive, plus import fees.
I doubt the existence of a complete New Old Stock system after all these years and much of what you find will be reproductions of the original.
It may be more effective to have a good local shop copy the existing exhaust system tubing and install it, supplemented with the NOS or reproduction hardware you find.
.