Triga,
These shocks are probably like most automotive ones, sealed either by welding or peening over, so practically unrebuildable. There will be some guys who say they can rebuild, but that just means they put new oil in them. While some seals and shims are often available, pistons, valves and glands are just not available.
I'm the Australian
Distributor for AVO shock absorbers, but I only service the shocks I sell. I'm sorry to advise, but I don't know of anyone else in Australia who makes one off shocks.
I have no listing for these cars, but I'll speak to the factory tonight to see what they know. They recently did a special run of shocks for old Vincent Black Shadow motor bikes, so I suppose anything is possible.