https://www.coronaviruspreventionnetwork.org/
It is a fairly long questionnaire - probably about 40 questions, mostly about your interactions with other people on a daily basis, some medical history, willingness to sacrifice your life for the benefit of society (just kidding on that last one) As I was filling it out, I got the feeling I won't be selected because I'm isolating to a large degree, and wouldn't be a good test subject.
I still have not seen a definitive list of test sites, but I'm fairly sure there will be one or two in my city.