The farmgirl groups are called Chapters and you can go to the chapter main page at: http://www.maryjanesfarm.org/Chapters/ On that page there is a chapter search function. Click on that an enter your area's info.
And no you don't need to be a member of a group to be a Farmgirl. Farmgirl is a condition of the heart- Farmgirls can be City Chicks of Country Chicks or anything in between!
If you meant the Farmgirl SisterHood- you don't have to be a member of a chapter to joing that either. Here is a link to where you can get more information about that: http://www.maryjanesfarm.org/farmgirl-sisterhood/