Hi, Adobe did not donate the Flex 3.x SDK to Apache. You would be much better off using the latest 4.x if you can.
But if you really need Flex 3.x try: http://blogs.adobe.com/flex/2012/05/looking-for-old-flex-sdks.html and run the Flex license SWF found on that page to select and download any version of Adobe Flex SDK. Justin
