Remember well over a year ago Adobe CTO Kevin Lynch demos Flash Player 10.1 on the Nokia N900? Yes ... but the problem is that it still hasn't materialised.
Here is the plugin on dropbox. To install it, simply replace the shared-object in /usr/lib/browser/plugins - but be sure to create a backup in the event that you need to revert. I suggest you move it out of /usr/lib and into /opt as it'll chew roughly 7MB of space. Restart browserd or reboot your device and you're done.