Do your research about IBD before you panic. The more you know the better choices you are equipped to make. Again, just because he vomited certain foods doesn't mean he can't eat them. I don't know that there are any vet specialists for IBD. Some vets just seem to know more than others. Another option is Pepcid, which a lot of vets will prescribe for nausea and vomiting. Pepcid and SE do similar things. So your vet might suggest that too.
Tomorrow (when this vet is in) I'll see if she knows what Slippery Elm is if she doesn't see if she can refer me to a specialist. I do have your link but have not read it yet. What he will eat after vomiting are those treats! but he can't live on those. I feel so bad for him because I figure he's hungry so I give him what he wants. Chances are that Montana won't like the taste, but who knows. Unlike Coony was, he's finicky about everything. I've never had a problem giving my cats Petromalt (for hairballs) but Montana won't go near it. I've had 3 generations of cats and never had a cat with a digestive problem like this so I'm pretty much at a loss. I sincerely hope I can do something for him....