I recently searched for an answer to how to see changes in Android Support Library between two versions and found out that I do not understand few things regarding Android S
You can use new Google Maven repo https://maven.google.com.
For example:
https://maven.google.com/com/android/support/design/26.0.1/design-26.0.1-sources.jar
Since that repo is new from support library 26.0.1, I'm not sure about old versions... But, for old versions, you can download the sources via SDK Manager, then find them in $ANDROID_SDK_HOME/extras/android/m2repository/.
I know you're not looking for sources. But this might help...