Here's a quick translation to English of the Central Bank reglementation regarding tourists/foreign exchange.
Sorry for the bad quality of the translation, not my native language & I'm in a rush today.
Translated from :
http://www.bcra.gov.ar/pdfs/comytexord/A5241.pdf
Quick translation and notes :
i. The sale of currencies for the purpose of tourism and travels to non-residents will be subject to an authorization by the Central Bank when the following requisites are not fully met: a) it is proven that the previous entry of the foreign currency through the local currency market during the stay of the non-resident in the country for an amount not less than the one being asked for by showing the original receipt of the exchange operation by which the foreign currency entered the country, and for which the process will be treated by the entity for the amount operated by the customer; and b) it does not exceed the equivalent amount of 5.000 USD for each customer and during the stay in the country. Copy of the required documentation shall be kept in the entity at the disposal of the central bank.
ii. Modification of point 3 of note “A” 4662, being replaced by the following :
3. “The purchase of currencies and the purchase of foreign currency bills will be done after approval by the central bank.
So, what this text means :
There are two cumulative conditions for a non resident to be able to buy freely currencies :
1- proving that the amount being exchanged has previously entered the country through the local currency market (the receipt needs to be kept) --> Example = John Doe enters Argentina with 2.000 USD, changes them to 8.500 pesos but at the end of his trip, he wants to change back 2.500 pesos to USD = he will have to show the original receipt
2- operation must be less than the equivalent of 5.000 USD (e.g. 5.000 USD/4.300 EUR/etc).
If those two cumulative conditions are not met -> the Central bank will need to give its approval.