I'm going to London for a game, where is the best place to buy tickets?

[fastforward]

I presume you've heard the news about the venue being switched. This will affect availability, (probably upwards), but tickets always sell out quickly in London, so if more tickets are available they'll sell fast. It's probably worth having a look on the NFLUK website. That's where the NFL does its London business so that's where ticket sales information will be. If nothing else you should be able to get decent information from UK based Seahawks fans.