I got flash working on my nexus 10 in two minutes with the boat browser.
Go to XDA and go to the Nexus 10 general forum, and look for the article: how I got flash working on my nexus 10.
In the OP, there's a flash apk, download that to your downloads folder on the sdcard. Then install it (make sure you have non market sources for apps in settings turned on.
Then install the boat browser. In the Boat Browser settings turn the user agent to desktop, and set flash plugin to always on.
Boom, i can now watch video on nbcnews.com. Genius.