As a retired US Citizen living in Buenos Aires, it is doubtful the USA Embassy actually has that kind of information. Granted, some Americans feel compelled to "register" as US Citizens abroad; however, there is no legal requirement that US citizens living abroad register with the USA embassy or Consulate. You'd do better talking with Argentina's Oficina de Migraciónes about how many American retirees live here.
When things become critical in a foreign country I've found the local US Embassy/Consulate to be of little value. For example, I was told by embassy "officials" last August that if I wanted to vote in the November mid term elections I would need to travel back to the State and district in which I was registered. Their reasoning: They couldn't be bothered by requests from all American citizens living here to manage absentee voting packets from all over the USA just for the mid-term elections. Last year was the first time I have ever had a problem with absentee voting in a foreign country. It seems to be a new policy.
The USA Embassy does offer certain services, such as notary public services for legal documents for your bank, attorney, CPA, or a court of law within the USA. They will also help you replace a lost/stolen passport, but not after being grilled as if you are being charged for a felony. If you get married down here and then try to get a visa for your spouse to enter the USA, expect to wait 12 to 18 months after which it will still be a 50/50 chance whether or not they will issue one. You can order an official copy of your birth certificate through the Embassy after filling out a long form that asks for personal information beyond your SS#, place, date of birth, and proof of citizenship. So always have your passport handy. The fees for most of these mundane services are rather steep.
If there is a civil war or coup, my personal experience has been to learn via local news outlets, (TV, radio, et al), that the local US Embassy "strongly recommends" all citizens to leave the country. They rarely offer help in traveling back to the USA or out of a country where there is trouble unless you or a member of your family works for the Consulate. So, plan to be on your own.
I do, however, strongly suggest that every US Citizen staying here for more than a few weeks pay the US Embassy a visit, if for nothing else the disillusionment. You'll discover the only place you are allowed access will be a small outer building that eerily resembles a Department of Motor Vehicles office anywhere in the USA. In that same spirit, USA Embassies, including the one here in Buenos Aires, are just as friendly. It's a very sobering experience for those who are traveling abroad for the first time. More than anything else, the USA Embassies are in place to broaden the USA's sphere of influence throughout the world rather than actually help its citizens living and traveling abroad.
Unless you're wanted for crimes against the State, (the USA(, don't expect too much.
i have to really agree with midlifebears final comments about the embassy. if you have any illusion that they are there to aid us citizens, forget it!!! they are there to help the immigrant to the usa. i went there when i had my legal crisis, forget it. no help. but im in crisis, had my apt. raided, had my phone tapped by the federal govt. i had to explain all of this in a crowded DMV type of building.
i called the embassy last week and spoke with several people who i could barely understand and although i speak English well and clearly, they could barely understand me. The recording you initially get has a thick accent.
They're not there for that either. Being a US citizen, you've never had to apply for a US visa. The common person -- be he American or otherwise -- simply doesn't figure highly in their list of priorities. And I don't know what those priorities are in Argentina -- if there are any.