Here’s a link where you can sign up. I got the information from Dr. Zorba Paster, so it’s not a crackpot site.
I already signed up for challenge trials elsewhere, no word on whether they’re actually going to be run though, or who’d be chosen out of the pool.
I signed up, but based on the screening questions I don’t think I’m likely to be picked (I don’t think I have enough exposure to help prove anything). I did read somewhere that they need like 120,000 volunteers, and have about 107,000. I’ll see if I can dig up what I read.
I came back here to bump this. The site has been updated and expanded since I first discovered it.