Windows 7 Professional 64 bit and Windows 8.1 Pro 64 bit on Parallels 11

Hi there! I am a little bit new to the Parallels forums so if this isn't the right place to ask this question, feel free to move it to another place.
I plan on purchasing a 13-inch MacBook Air with an Intel Core i7 processor, 512GB of flash storage, and 8GB of RAM and I plan to run Parallels Desktop 11 on it for college. My college uses both Windows 7 Professional 64 bit and Windows 8.1 Pro 64 bit so those are the 2 operating systems that I currently only plan on using. I'm wondering if you guys know where I can buy the right copies of these operating systems? Are there any right ones that are on Amazon and/or eBay? I would appreciate links to the right softwares for me to use so that I don't make a mistake.

 

If you are registered to a university/college it may be possible to access for free through dreamspark or similar solutions.

 

If for some reason you cannot obtain them through your school, you can still get OEM
disks here:
http://www.newegg.com/Operating-Systems/SubCategory/ID-368
and various other vendors.

I would avoid Ebay as many people sell pirated or otherwise unauthorized versions
of Windows OSes.