Tomahawks very much were trade items from the earliest days of commerce between the Europeans and the Native Nations, being a stock item for the fur trade . There were roughly two kinds.

There were utilitarian little hatchets, sometimes now called "Squaw axes", forged of iron usually with a piece of steel welded on to form a sharpenable edge. They're often quite small- perhaps a blade of 2" or so- but were immensely handy tools for knocking apart brush for fire or dressing out a deer. These have been recovered in many archaeological digs, often showing signs of very very long, hard use. Not only the Native Nations used them, but they were very commonly carried by the Colonist hunters as well. George Washington , on receiving volunteer riflemen into his army, thought them a very, very poor substitute for a bayonet.

Then there are the more ornamental trade tomahawks. At some point around 1700, they were commonly made to be both pipes for smoking and tomahawks, and they became quite a prestige item, like the one in this fine portrait of Thayendanegea ( Joseph Brandt) by Romney. The two forms could overlap a bit: you can see in this group the utilitarian hatchet has some ornament. But there were some quite fine presentation tomahawks made, like this one circa 1760. Circa 1800, a new style was introduced- cast brass head, sculpted, turned and engraved, with a piece of steel dovetailed in to make the cutting edge. You can imagine the traders rubbing their hands, thinking "right, they'll all want to have new ones, now".

They were sometimes made by gunsmiths: we know, because occasionally the gunsmith would put his name on one. They were quite likely imported as well, especially in the early years of the colonies, when there was little colonial manufacturing of anything, but how much overall is uncertain. There is a real possibility that they could have been made sometimes by Native Americans themselves, but though that's attractive, the Nations that would have been most active in the fur trade would not have been likely to do that. They would have been on the move very often, and, as can be seen in the examples, some of the designs are quite sophisticated in ornament and execution and so the product of a well-furnished, non-portable shop. ( you could ask now, why build your own car when you can earn money to buy one?) But at least the Cherokee and the Iroquois had adapted and adopted much of the colonists' lifestyle by the later 1700's, so who knows?