Hi Lori - I'm so sorry that your husband is so sick. I don't know of any specific "gurus", but I know that a few cities in the US have experimental gastric pacemaker clinics. (I think there's one in Southern California, and another maybe in Texas - I'm sorry I can't be more specific!) But, I reckon that if you looked up the pacemaker, you could find the clinics, and there would definitely be gastroparesis specialists there.
I have gastroparesis too. I'm really sorry about your husband - I hope something works out!