This is not a simple issue.
I don't believe there is any chance of a single bank here offering the sort of guarantee mentioned above to a foreigner, unless you have been here for quite awhile, have a long history with the bank, all residency stuff correct, etc. I would be seriously surprised (I've looked into it). Maybe at the levels of people who have so much money that it rarely seems to matter what country they are in, they can always make deals with banks through the pressure of their own weight from their home country (I actually know a couple of guys who do have that kind of pull, even here, at least with City Bank and through American Express).
You have to be a client of the bank. You have to have a DNI. You have to fit in one of the categories mentioned. I don't think banks, or other guarantor companies, will be the route you are looking for.
Rich One also mentioned buying a "fake guarantee" from a shady company. Not sure what he means by fake, as they would be real guarantees or they wouldn't work if they were fake (although there are people out there who will offer guarantees that won't work, take your money, and then shrug their shoulders sadly when it doesn't work out and laugh when you suggest they return the money, if you're not careful). But there are companies that arrange for you to have a guarantee with owners of properties who are looking to make a little money and offer their property as guarantees. This is not really 100% legal (maybe what Rich One meant?) but it is knowingly done.
I've been confronted with the near-term probability of having to leave my current apartment at the end of my 2 year lease and have been looking at this and found these guys as an example:
http://www.garantiaalquileres.com.ar/
I am not suggesting them as a source, simply because I haven't looked any further than their website. I don't know if this really works or not.
This whole guarantee thing has to do with the wonderful laws of this nation which are designed to protect the "poor and defenseless", but which actually do no such thing and in fact hamper business and residential accommodations. To me, it is one of the greatest banes of existence here.
The problem is that if someone stops paying rent, it is very, very difficult to get them out of a property legally. As far as I can tell, there is little difference between commercial leases and dwelling leases in this regard. The guarantee is "traditionally", literally, another property being put up as part of the lease contract (yes, the title of the guaranteeing property attached, with defined penalties, to the contract), to act as leverage for the owner renting his property to use if the renter doesn't comply with his contract. It is possible the owner of the property offering the guarantee could even lose his property for having guaranteed the rental contract.
This obviously makes it very difficult for someone to want to put up their property as a guarantee for someone they don't know, or don't know very well. Most garantias are preferred to be from CABA (or, in the zone where the rental is) and be familiar (i.e., the person who is guaranteeing is supposed to have some relation to the person renting so the person renting feels some need to not screw over the person guaranteeing as well, although I've heard of plenty of cases of family relations screwing each other over on these things anyway).
I've been lucky enough to not have had to have a familiar relation in the garantias I've found, and twice the properties were not anywhere near CABA (one in Cordoba, the other in Mar del Plata). The last garantia I got was through the parents of the boyfriend of a friend of my wife's and I had to pay two months' rent for it. Now that the owners of the apartment we're currently renting are looking to sell the apartment I rented with that garantia, I am looking for a new one myself again.
As far as what defines the guarantee - nothing in particular is fixed. It is not any kind of law that requires a guarantee, but rather what practice has been mostly adopted to protect owners from rampant abuse of the legal system to get out of paying rent or paying for destroyed property. The inclusion of the title of another property (between owners, this is, not renters, you have to understand) in a rental contract has simply become the standard way that owners have found to protect themselves.
Some owners will accept far less than the value of the rent over the term of the contract, up front, in lieu of actual property, in the form of additional deposit. I was looking at renting a place not too long ago, for a verduleria, that would have allowed me to pay 4 months' deposit in lieu of a garantia. It all depends on what the owner is willing to accept, and often this has to do with the type of property, where it is, how much it's worth, etc.
BTW - an actual commercial lease is three years, not 2 years. Sorry if you were already aware of this, I just noticed you mentioning paying two years' rent up front, which coincidentally is the length of a long term residential rental agreement. Maybe the owner you were talking to would have accepted 2/3 of the entire rent instead of all three years, I was just making sure you understood the difference in terms between commercial and residential.
Beware that no matter what your rental contract says, there are national contracts which are predefined and you cannot make any agreement that is in contrary to the contracts predefined by law. The law here specifically states this, that you cannot agree to anything that would change the nationally-defined contract. You can add additional terms, to be sure, but nothing that reduces or contradicts what the current law states. The parts of a contract that you signed that don't agree with these predefined legal points are null and void. If you are renting a place as a commercial property and only have a 2-year contract, for example, the owner can turn around and make a claim that you still owe him another year on the contract after two years, which means that if you wanted to conclude the contract in two years, you would have to pay penalties for breaking the lease early (also defined in the law) and if you had a guarantee, the guarantor is on the hook for anything with which you don't comply.
This whole lease/guarantee thing (both residential and commercial) are to me one of the biggest things seriously hampering business and living in this country, and not to the benefit of anyone, particularly not to the poor and defenseless which are supposed to benefit from such things. Right along with the horrendous labor laws that put so much weight on the businesses, not to mention a host of other issues to live and do business here...
