You don't-
What you do is find a reputable financeria that has money outside of Argentina.
They wire you the money there either with by you handing them your money and they wire it out from a diff account they have offshore, or they wire that money for you from here.
If you want I know a reputable place who we work with and do these kind of transactions.
We have used them to wire money in and once we have a confirmation it went out within 3 days they get it here.
Of course they charge a commission but its not bad at all.
Have to see how it works if you give them money and they wire it (as many people reading this will ask- well how do you know they won't just steal your money and never wire it?).
The best thing here is that you give USD and get USD on the other end.
The other solution is have the buyer wire the money from offshore to offshore and never give you cash...or through an escribano who has the right contacts with an institution as mentioned above.