It's a free download from the Silicon Labs website. With SimplicityStudio v 4, PC Controller was a part of the download. With SimplicityStudio v 5, PC Controller has to be added from the menus as a tool, which downloads it. PC Controller does not run on the Mac except in a virtual box. There's a thread on the forum here about how to install it in a Mac virtual box.
The native Simplicity Studio v5 for the Mac does not have PC Controller.