It all depand , for what boat you need rub rail . There are many different . Aluminium trading in Joburg have some , they are on their website also , but you have to take it for anodizing also.
Maybe best is to phone one of KZN boat manufacturers and ask where they buy it . FG marine ( Seacat ) told me they get it from Durban company .
I hope you know how to bend it without kinking it . Ain’t simple job .