Maybe from turists? I don't know about Argentina - but in cases like this turists are often forced to buy the local currency by using the official exchange rate.
Martin, you have to understand that many people from other countries do not use cash most of the time and are used to be able to get a fair exchange when using their Credit/Debit cards in other countries.
These people, not having found out the state of Argentina (keep in mind that find out about all these in english is even harder than in spanish) will not arrive with much cash to exchange. And this is not a hypothetical, I've seen this a couple of times already.
