old flex sdk download
apache-flex, sdk
Solution
I just came across this from @zwetan for downloading 4.5.1:
http://download.macromedia.com/pub/flex/sdk/flex_sdk_4.5.1.zip
For older versions, I believe you can just adjust the url, so if I wanted 4.6, I just used:
http://download.macromedia.com/pub/flex/sdk/flex_sdk_4.6.zip and it dl'ed.
I don't know if that'll work for anyone else, but it's working currently for me. I will now have my own copies for a bit.
Problem
Since old flex sdk download links don't work, and question https://stackoverflow.com/questions/10456540/where-else-find-a-download-link-of-flex-sdk-4 is closed, maybe somebody have some other (private) link ... ?