Its rare that a manufacturer does not offer A/C as a factory fitment for the cab since the early 90s. It just depends on the local market as to whether its fitted or a larger heater matrix is fitted instead of a dual heater/A/C matrix. Wreckers for that vehicle type in Southern Europe may have the lot, you need brackets, engine pulleys (usually all of them, maybe water pump and alternator pullies as well), air con compressor, condensor, front cooling radiator, electric fans (usually), drier, wiring harness, in dash evaporator, piping, through firewall piping gromments - about it. Some automatic gearboxes also require a valve mod to stop the gearbox kicking down at inopportune moments.
12V/24V will depend solely on your vehicle alternator output - unless you are thinking about solid state peltier type air con - in which case dont as its not yet been proved successful in comparison to gas filled units.
The other 12V/24V options are Swampy Coolers which basically use cold air from ice in an esky box and blow cold wet air all over you, which is great in hot dry climates, but like driving in a sauna in hot humid climates.
Aftermarket A/C (cheaper) is usually a case of fitting eg
Under dash COOL ONLY with vented fascia: Speedy Air Spares or
Under Dash Air Conditioner & Heater with Vented Fascia: Speedy Air Spares
you then add all of the above and maybe have to make up brackets, etc etc. The same website has complete kits to give you an idea of whats needed.
DIY fitment is possible, but an absolute pain in the arse, I'd cough up and pay someone else to do it, fill the thing with gas, etc.
Average A/C compressor will take 10HP from the engine so expect performance and fuel to suffer.
You can run some roof top A/C units by ffitting a large (3,000 to 6,000 watt) inverters and adding a high output (200amp) alternator (a Dutch company DC Airco has off the shelf units) or dedicated 12V/24V generators to power the inverters.
You could run a suitably sized 240V genset but the safety issues need to be really well thought out, cable shielding, earth trips, fusing etc.