Sorry it is not available! The simulator will only allow you to install programs from xCode. I am not sure why they restrict this - but I am also not sure why you would want to use the Simulator for this purpose.
It's a simulator not an emulator. Even if there was an App Store in the Simulator, none of the apps in the store would work since they are compiled for ARM CPUs while the Simulator runs x86 code.
Probably wont work, but if you have an IOS device and copy an app onto your computer, you might be able to run it on IOS simulator, as you can run your own apps.
You can put application in your simulator. But you cannot run it. They have restricted users to run applications. I found where the .app files are.
Machintosh HD - Application - Xcode - Contents - Developer - Platforms - iPhoneSimulator.platform - Developer - SDKs - iPhoneSimulator.sdk - Applications
All applications are in there but, I can't run them. However, I succeeded to install .app files.
In .ipa file, there is 'payload' folder, and .app file is in there.
All you need is just copy it and paste it in Applications folder. Then you can see the icon on your simulator.
But, it will not work.