Today I had the need to decompile WP8 assemblies so I tried to load System.Windows.dll from
C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\WindowsPhone\v8.0\System.Windows.dll
with Reflector but I found that all methods and implementation was empty!
So I started googling and I found How to decompile WP7 assemblies from Benjamin Roux. He was having my same issue but for WP7.
Thanks to his solution I was able to find the dump of WP8 on XDA Forum too on, well I think that if you mount the emulator virtual machine as drive you can even get it but I had my vm running so I decided to download the dump and I was able to find System.Windows.dll on WP8Dump\3\Windows\System32 now loading this assembly on Reflector did the trick! All methods and implementation are visible !
Now I can try the right solution to my starting need: detect compression (end of scroll) of a ListBox but I will discuss this I an other article.
Hope it helps