So there are two places you can get any of these from: apple, or a cached copy at edgesuite. The first part of the url is:
http://appldnld.apple.com/ (normal downloads from apple) http://pfd.apple.com/ (protected assets from apple) http://appldnld.apple.com.edgesuite.net/content.info.apple.com/ (both, cached version)
Combine one of these with the url fragments listed below to create a full link.
You can't download a protected assets link without a download key. These change often.