Fitting of air conditioning in W460 model

Simply, you will not find any. But that does not mean it can't be done. Expensive it can be.

Problem is no one does the kit for the vent blower kit any longer; if you care to hunt for old Porsche vents, some have fitted these to the W460. Or get similar ones which is possible but the unit sticks out like a sore thumb. 

Cheapest alternative is fit a roof type unit as done in motor homes; this means carrying a hump on the roof at all times limiting most multi-level car parking or ground leveled ones if controlled by height.

Although I am not sure on this but I don't see why a W463 blower/vent unit cannot fit into the W460 dash, costs with standing.

I guesstimate a cost of this exercise to be between £4500 to £6000.