My son, who is 12 years old, was recently diagnosed with gastroparesis. If you live anywhere near VCU in Richmond, VA, they have two doctors who treat pediatric gastroparesis.
I second CalGal's suggestion. I would also advise to find a gastroparesis support group, online or off. (Yahoo groups has a pretty good GP group.) This way you have one place with a large concentration on people who are knowledgeable about the condition as well as about new treatment options and doctor recommendations.
I'd suggest you check with the closest university-associated teaching hospital in your area. That's typically where you'll find docs who are up-to-date on a broad range of GI issues.