Download the A10 module and DCS world and you should be able to fly that with us
If you want the fly the mustang in a mission, just buy, download and install that module in DCS World.
DCS World is the core game, containing all the units etc.
The individual modules contain the cockpit data and such, thereby, you can fly in any mission provided you have at least 1 of the planes types.
Although I can heartily recommend the Mustang, sure is the nicest prop aircraft I have seen in a game.