Your options are, go to http://get.adobe.com/flashplayer/otherversions/ and install it yourself using one of the versions or use a script file to install Flash Player on your system.
The script file can be downloaded at http://web.techfurs.net/Flash11ForUbuntu.html then follow the directions so the script will install it for you.
If you need any help or have questions, feel free to comment.
Edit: Updated on March-12-2012. Fixed link, updated page, updated software to 22.214.171.124.