Finished and not, different sizes and more;
http://www.powderhornsandmore.com/index.html
More places for horns;
http://mman.home.att.net/PowderHornsForSale.htm
http://stores.sheasmtn.com/Categories.bok?category=Powder+Horns
Article 1 - History of a Powder Horn
Article 2 - About Powder Horns