Well, when I started Dr. Sketchy's, I advertized it on alot of illustrators communities. People started writing to me to bemoan the fact that there was nothing like that in Salt Lake City or Viriginia or wherever they lived. So, I wrote a tutorial on how to start your own. Within a few months, I had five branches. I sat down with a lawyer, wrote a licensing agreement that spells out their obligations and what they have to do.
Fast forward a few months. I get a book deal for Dr. Sketchy's. Me and my friend John write a book on how to start your own branch (with lots of paper dolls and drinking games thrown in). It starts spreading like wildfire. Every week now I get about five requests to start branches. I don't run them myself, but I work closely with the folks who do, and sometimes I work on projects with them. For instance, me and the Edinburgh branch brought Dr. Sketchy's to the Edinburgh Fringe Festival (21 sessions in one month), and me and the San Diego branch did a big afterparty for Comic-Con together.
Here's a fairly accurate map of all the branches (I know we left a few out)