you can find some of them on html5gamedevs.com in the sponsors forum, but everyone can see these emailadresses so i think the people get spammed a lot and so dont reply to many offers (i only got one deal there)
about half a year ago i emailed every sponsor thats listed there, got more "email adress doesnt exist" then real replys and made one sale (to a sponsor that just arrived there, they are "overfed" now too :/ ).
there are two dudes that SELL theyre lists (google "making money with html5" or neoprofessor, they are both on this forum here, the guy that sells the "making money with html5" book claims that he made a lot of cash with his games but when you look at his games.. they are not too bad but also not great, i cant really believe all these numbers he posts), i dont really trust that these contacts are different from the ones you find at html5gamedevs.com, even if its not the same contacts i think the problem is the same, many people get these contacts so they get picky or even shut the whole email adress down and dont reply.
im not alone with this opinion, i did read many times that people say "search for gaming portals and contact them", i think thats a good strategy, but like you said, a lot of work and i didnt found the time so far to do it. From my sight its hard to find sponsors but even on FGL.com its not easy to make sales. Hard business when you dont have a really really good game (my games seem to be not so good ^^)
Edit: i stand corrected, just made my first non-exclusive sale over FGL "old" gameshop