In the US 16"x6" mirrors were standard for many years and they are available everywhere. The Grote number is 16202
https://www.ryderfleetproducts.com/grote-16202/west-coast-mirror-head-6x16"-black-economy-p-w38-16202
A 450 should have been fitted with a type 9 chamber. Haldex still makes them.
https://www.ryderfleetproducts.com/haldex-sc09/brake-chambers-type-9-p-v19-sc09
