Abdominal pain is really general, and finding a specific specialist will be difficult. Usually if the pain is super bad seeing an emergency physician is the best option. However if it is not troublesome, trying to pinpoint the problem and doctor, should be your primary care provider.
Here is a list of all the doctors you cold potentially see with acute abdomen; Hepatic, Gastrointestinal, OB/GYN, Nephrology, Urinary, Oncology, Vascular.....