From Adobe Labs
There are three ways to get the source repository:
1. Check it out using Subversion. If you have Subversion installed, run the following command:
svn checkout http://labs.adobe.com/subversion/flashplatform/
2. Download the nightly build zip file.
3. Use the source repository browser. You can view both HTML and text version of the source code.
This source code is licensed under the Adobe Systems Incorporated(r) Source Code License Agreement.