Windows 8 comes with a few new fonts, fonts that I would like to use or have for editing PDF documents that did not have the fonts completely embded.
Is there somewhere I can download these new fonts?
You generally can't - the licence to use these fonts comes with the OS, and the only real way to use them legally is to either buy and use the OS or products which contain the fonts, or to buy them directly off the foundry that designed them. Microsoft has a site with the fonts it bundles with windows 8 linking to monotype where you can buy licences.
The MSTT Corefonts are an exception - they were released under terms that allowed them to be redistributed under terms that were not totally free, but loose enough that they could be used in other OSes - and MS stopped doing this cause of licensing issues.