Someone makes them. I saw one two weeks ago at ASU's Summer Camp in Washington, D.C. I didn't get a chance to ask the aikidoka where he had gotten it. I suppose I could track him down, since I think he trains at Aikido Shobukan Dojo.
I know that Osage orange is one of the woods Unka Kim offers...it is quite a bright yellow when it is brand new, I've heard that it fades to a brown/yellow over time.