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You can always get the socks

http://www.revolushonsportswear.com/#!store/c1x37

Found one but already sold out:

http://www.reddit.com/r/Seahawks/comments/2mbqb7/voler_selling_a_12th_fan_cycling_jersey/

I haven't seen one yet. We did see a cute couple on a tandem on Whidbey earlier this year wearing Hawks jerseys. They had a large 12th man flag on the back. Salsa, was that you? :)