You should try the BetOnline free rolls they have them every hour. Carbon poker sent me an email giving me 5 dollars for free, I don't know if they do that for everyone but, you could try joining.
i like very much playing the freerolls on fulltilt bankrollmob small field then pokerstars on FT is max 1000 and on Pokerstars 4-5k i managed once win 1st place on FT for 5,40$ i play more night around 12:30 max 400-600 players
Well, depositing also enables much more freerolls, adds some free tickets etc.
But I really dont know how its working from US.
What about 888poker and their 24/7 freeroll + some first depositors freerolls etc.?