Where May I (legally) get a Mac OS X .iso File to Virtualize OS X?
These steps assume that you already have purchased OS X 10.9 through the Mac App Store.  


Open the Mac App Store  
Press the Alt Key and hold it during the following steps  
Click at the purchased tab  
Scroll to OS X Mavericks  
Click at the Download button  
If you already have OS X Mavericks installed, you will be asked if you want to continue  
Click continue  
Now, you can release the Alt Key


To get the dmg file:
1. Go to the downloaded install application in the applications folder
2. Control+click on the installer, and choose Show Package Contents, and choose Show Package Contents.
3. Navigate to Contents &gt; Shared Support
4. The file you are looking for is called InstallESD.dmg

If you need a .iso file, you have to convert it using Disk Utility