Dave has asked an interesting question. Going right along with that question is where did all the leather come from. There was an immense need for leather in the colonies. For every horn shop or horn factory in the colonies there had to be at least one cordwainer"s shop, one harness shop and one shoemaker's shop. It is only a guess, but I suspect there would have been more than one of each of these shops for every horn shop.
During the 18th century the most common breed of cattle in the American colonies was the English Devon Red. This breed is the "triple purpose" cattle breed that James talked about above. Devon reds were beasts of burden, producers of milk, pulled wagons and plows and thrived on forage while requiring little feed to be supplied by the farmer. What they weren't raised for was meat, horns, and leather. If one did die or had to be put down the farmer would most likely use the meat, hide and horns for himself and his family. I suppose that if you had a couple of extra yearlings, especially bulls, they might have been sent north with the large 18th century cattle drives, but that was not the main purpose of having and raising the Devon reds.
I am a maker and student of 18th century powder horns. Especially the large double twist/curve powder horns made during the French & Indian War and up past the Revolutionary War. The Golden Age of engraved powder horns. I have been privileged to inspect and handle many of these types of horns. When I look at the large double curve horns I don't see ox horns or Devon red horns, I see Texas longhorn cattle horns. The Texas longhorn was not a breed of cattle that existed during the 18th century, but their ancestor, the Spanish Corriente or Criollo breed existed and was brought to the North American continent and to almost all other Spanish colonies in the 15th and 16th centuries. The horns on the Corriente look like Texas longhorn cattle horns. Large horns with the double curve or twist. Large herds of these cattle existed in Mexico, California, Florida, and what would become Texas, not to mention all the Spanish island colonies like Cuba, Puerto Rico and others.
William Guthman, who wrote a well respected book about French & Indian War engraved powder horns indicated that, tons of leather hides from Spanish Corriente cattle were purchased and imported into the American colonies. As there is not much value in raw horns, the horns from the cattle that supplied the cow hides were shipped along with the hides for little or nothing.
If Guthman is correct that explains why I see Texas Longhorn steer horns beneath the engraving of all those 18th century horns. This might also answer Dave's original question about "Where did all the horns come from?"
Randy Hedden