My insurance plan has a Nurse Direct progam that helps people find a doctor. If you have a program like this you can call and tell them you want a doctor who treats patients with IBS or other digestive orders. Information should also be available about age and how long they have practiced.
My GI's office recommended my current GP, because they were impressed with him and also suggested him because he was just out of med school. My GI's office feels newer doctors have more knowlege about nutrition and drugs than older ones.
My GP was the first one who suggested I keep a dairy of my food and how it effects me. This was at the same time I discovered Heather's book. I'm really happy with my doctor and he follows up with me every six months, which I've found others doctors don't. My last visit was two weeks ago and he said I'll see in six months, unless you are having problems make sure you make an appt.
Do your own research before you see a new doctor. The health clinic I use also has a list of their doctors on line and gives a brief bio of each doctor.