Private organizations are involved in similar actions to Quantum all the time . The Wonga Coup is one such example, though it admittedly failed. Organizations like Executive Outcomes are fairly similar to Quantum, though they're clearly not as far reaching.
Juan Cole has a long post about the evolution of James Bond from left to right, which I recommend. (Warning: spoilers ahead)
In the new film, Dominic Greene is a secret member of Quantum, a mercenary coup-making consulting firm. That is, it is represented as a private contractor to which the CIA is willing to farm out coup-making instead of doing it directly. Greene's cover is that of the head of a conservation organization that buys up land in poor countries to ensure it is preserved from despoilment. In fact, he despoils it. In a complicated and not very plausible plot twist, Greene appears to be buying up land under which he is convinced there is oil, but in fact is trying to corner the market on Bolivia's aquifers so as to overcharge the country for its water after the military coup unseats Morales.
The CIA is convinced to back Quantum both because it wants leftist governments in Latin America overthrown and because Quantum would re-privatize Bolivia's fossil fuels. Greene observes to CIA field officer Greg Beame that the way the Bush administration bogged the US down in the Middle East allowed several Latin American countries to move left (obviously, the referents are Venezuela, Bolivia and Brazil).
Though the parts of the actual plot hatched by Dominic Greene are far-fetched, but not as much as you would think. The films villain, Dominic Green, has hatched a scheme to engineer a water shortage in Bolivia. This plan (reminiscent of Noah Cross's scheme in Chinatown) is clearly inspired by the actual water privatization
in Bolivia undertaken at the behest of the IMF.