There are people you can give your USD here and they then transfer USD they have abroad to an account of your choice. The transfer is called a "cable". I do not know such people personally, but I know people that send money outside of Argentina this way. You just need to know trustworthy people who do this.
Alternatively, you can go back and forth to Uruguay, deposit your money in a bank there and then transfer from there, though this is obviously not the ideal situation. You could take 3 friends and with a car cross the bridge in Fray Bentos and take 40K and open an account in a bank in Mercedes.