What's the best way to find a US citizen who will marry a foreigner for green card?

The best way is to keep advertising clearly on the internet. Make sure you explain that the only reason that you want to get married is to get a Resident Alien identification. It is very important to be clear about your intentions and to state if you are willing to pay this person. You should also give your full name, country of origin, age, sex, race, date of birth and email address. It is only fair to the person who answers your request. (Oh, and it will also make it easier for DHS to find you since it is a criminal offense to marry solely for Immigration purposes).