Hi
Carmakers like Fiat will almost certainly have bought in the connectors from an external supplier specialising in such things. Unfortunately, there are so many variants that it is very unlikely you could buy replacements other than via Fiat.
A scrapyard is one possibility.
If you only want to connect to a limited number of pins for testing purposes, I suggest you buy individual mini blade connectors from someone like RS or CPC and solder them onto thin test leads. A layer of heatshrink sleeving will guard against short circuits.