Apple now allows you to run OS X inside a Virtual Machine as long as the host is running Apple hardware. Because we need to test our web site on various versions of Safari, we picked up a Mac Mini running Yosemite for testing purposes. The idea is to run Mavericks (currently our largest user base) and possible Mountain Lion in a VM on demand, similar to what we do on our Windows.
However, I've yet to be able to find a place to download prior installer apps. I've found other StackExchange posts referring to the App Store, but since this is a new Apple ID there are no previous purchases for old versions, and as far as I can tell they are no longer available to "purchase". Likewise, I have not been able to find any OS X Installer apps on the Apple Developer site.
Am I missing something? Is there an easy-ish way to get these apps to install OS X to a VM?
(For VM host, we are currently using Virtualbox, but would be willing to use VMWare or Parallels if needed)