I doubt any of these guys that build Asiatic horn bows are familiar with Ilex vomitoria because it is indigenous to the coastal areas of SC, GA and FL and no where else that I'm familiar with. I used to live in Coastal GA and SC so I am familiar with it and it's use in Black Tea. I am, however, not familiar with Asiatic horn bow core woods other than mulberry that, I believe, is a traditional wood used. Dave has suggested other woods that would probably be appropriate.
As much time and effort that goes into these horn bows I think I'd stick to the tried and true woods.
Where do you live, Chuck?