Where To Get The Debug Flash Player Installers
This link at Adobe has a list of archived Flash Player versions from Flash 8.
Debug Players supports the “trace” command (while Release version does not) by writing to a log file.
To see trace outputs, you can open the log directly (using a text editor), or use convenient tools like Flash Tracer (a Firefox Plug In) or Alcon (works on IE and Firefox).
Where To Get Installers For Older Flash Players
This link has even older versions of the Flash Players, all the way to version 2.
Where To Get Flash Player Uninstaller
Useful if you need to install an older version or to see how a site behave without a Flash Player.