You get dollars the same way anyone else would in the situation: You carry a trade surplus vs. the United States and then allow tax payments to be made in dollars. Prices settle as a function of dollars available, rate of circulation, and volume of goods & services available.
The policy should produce a boost in exports & employment but also produce a shortage of goods normally imported. It'll also be a great time for Americans to visit, the dollar suddenly having a lot more purchasing power in Argentina.