No I don't think you could get a referral for an ob now (you would need to be pregnant to get that referral) but I thought if you explained the situation to a good GP they might be able to give you a few names of obs that they consider good that you could contact and have a chat with?
So did you see an Ob with your first 2 pregnancies? I am not really sure but from what I know of obs that I and my friends have used, I would have thought all of them would (and have) prescribed maxalon or other meds to some one in your situation. The search may not be as hard as your think, I think the number of obs who would help you would be fairly high? Some of the others in this thread might have more information on this?
BTW did you ever go to hospital due to dehydration when you were pregnant? I would think (hope?) that if all else failed and you went to hospital they would give you something to help ease the vomiting?