Parallels doesn't recognize Windows 8 Bootcamp
I have searched high and low for this one.. turns out that there is a way to manually configure a VM from your bootcamp partition to appear within Parallels running in OSX even if the option to use an existing windows installation does not get displayed.

Check this out - http://kb.parallels.com/en/112941

Essentially what you're doing is pointing a new parallels VM file to the partition on the HDD/SSD that has the windows boot loader.