OKN, the way I see it, 404 traffic is not your best quality traffic. I mean, how much 404 traffic can you have? Just a tiny little bit... as long as you don't delete sites after you submit them... which I want to think you're not doing.
Now finding a good sponsor... that can be tricky. There are loads out there, you need to see which works out for you. Sign up and send some traffic to a few of them, there's a list here
http://www.greenguysboard.com/main/welcome.html and there are a lot of banners on this board filled with good sponsors...