For the standard set up I'd regard these as a "special", a BSA hose rather than a generic one. For a filter add on any hydraulic hose outfit can make you up a plain pair, the armoured feature is the special aspect. These hoses carry very little pressure, the armour is to just to protect the hose. Braided hose is an alternative, but for the genuine look it will have to be parts from one of the usual classic bike suppliers and then a bit of fettling to fit non standard connections.
C & D Autos at Henley in Arden used to do the standard pipes, don't know if these folks are still in business, website looks untouched for years....
Swarfy.