de Haro Horns
Custom horn leadpipes, repairs, screwbell conversions, valve rebuilds, accessories, maintenance products, and replacement parts; tutorials for horn players and a suggested reading …
hornsAplenty
Specialize in selling fully-reconditioned, professional models (Paxman, Alexander, Schmid) of used French horns.
Hoyer, Hans
Official site (in English) for this professional horn maker. Includes descriptions of all professional and student model horns.
Patterson Hornworks
Makers of custom french horns and natural horns. Mouthpieces, leadpipes and complete restoration also available.
Seraphinoff, Richard
Manufactures historical reproductions of Baroque and Classical natural horns.
Thompson Edition, Inc.
Horn cases, mouthpieces, mutes, sheet music, method books, and the "Thompson Edition": a collection of reprinted original orchestra parts.
TrumCor Mutes and Music
Hand made mutes and stopping mutes, as well as some music for horn quartets and brass quintets.