Sadly they don't if you want a headlight for a 2005 Fiat Panda, (same car/style still in production today).
FWIW I work for a company that shares some vehicles with Fiat, in the same way as the Citroen C1 and the Toyota Aygo are the same car, (mechanically at least), and you might be surprised at how many people come to us because the Fiat dealer can't find the part, or they can't get the part, and our price always beats the price Fiat have quoted, (according to the customer anyway).
We actually sold a 500 last winter, (screaming yellow it was

), and it had actually had stop/start to get back to the OP. The guy brought it back as the stop/start was not working. We found no obvious fault, so we sent it to Fiat for diagnosis, their response was, nothing wrong. It transpired that because the owner had the audacity to use his heater, heated rear window, and possibly even his radio, (shock horror) during the old weather, that if the car had cut the engine the system did not have enough reserve to re-start it. So if you buy a 500 with stop/start don't expect any fuel savings if it's cold outside