Funny you should mention powder horns. In either CdA or Post Falls is a fellow named John Nelson. He makes a pretty good powder horn, assuming he has any cow horns in his supplies. I do not have his contact info, but it might be fairly easy to find. If John is not able to help you with that, I would then get in touch with Gerry at Powder Horns and More. You can google that. I know he can fill your order PDQ. He can also provide you a nice cow horn or two for when you make your own. He would be my go to guy for this.
Hope this helps.
John (Bigsmoke)