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.
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.
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.