Search the app store. There are several alternate browsers that advertise the ability to play Flash content. However many people report very mixed results since the way these browsers work is to send the Flash content to a server to be converted to iOS format and then sent back to the browser. The bottom line is that Flash has never been supported on iOS so take that into consideration.
Most of the big web sites have long since supported iOS for video. I watch video clips, YouTube, etc. all the time on my iPad and don't really run into many sites that won't work. I'm sure there are and the best course of action is to encourage those sites to get with the plan and support mobile platforms like iOS and Android.