Although yours is a bus chassis, most of the components were common with the truck chassis variants.
The J engine (previously known as the 5 engine) is the 330 diesel 6 cylinder, so almost any model fitted with this engine will be the same, and brakes will be common with the appropriate GVW range truck (at a guess KC/KD or maybe KE - EJM or EJN models in the later designation).
Suspension and steering will again be common with similar range trucks as would the electrical systems. The only differences will be the location of some of the components.
Major differences occur when models have airbrake systems instead of hydraulic brakes like yours, but they are the heavier GVW range models. Even VAL (the six-wheel coach chassis) would have many parts common with your 'VAS' such as the brakes.
If you visit a classic truck or steam-engine rally where there are 'car-boot' type sellers you will probably find what you need.
Try the Great Dorset Steam Fair later this month (29th August to 2nd September):-
http://gdsf.co.uk/
You might enjoy the other events at the GDSF too . . .