I need a version older than 3, but newer then 6. (and don’t you dare give me 6.1!) THX 
previous version available here http://unity3d.com/unity/download/archive
but you can use following google query to find older version
url:http://download.unity3d.com/download_unity/ +unity VERSION_NUMBER_HERE
and as you will see most links are pointed to answers.unity3d.com
anyway here is a set of previous version