Given the small number of rifles ordered by Campbell, I tend to think he may have had in mind selling them to his tenants on the 20,000 acres of land he was subdividing west of Saratoga, NY. His orders for goods intended for the Native American trade were generally quite large. For example, for the 1772 trading season he ordered 10,000 flints, over 4,000 lbs of gunpowder, and about 185,000 "Fusil balls 28 per lb". Also about 7,000 knives. If I have a chance I'll take a look at his letterbook for the orders Bailly cites and see if there are any clues as to whether the rifles were intended for the Native American trade.
That said, Sir William Johnson (Commissioner of Indians for the Northern Colonies, headquartered at Johnstown, NY just north of the Mohawk River) submitted a departmental report to the Lords of Trade (IIRC) at the conclusion of the French and Indian War in which he advised prohibiting traders from supplying Native Americans with "rifle barrelled guns." The text reads: "Art 38th: Rifled Barrelled Guns should certainly be prohibited; the Shawanees and the Delawares, with many of their neighbors are become very fond of them, and use them with such dexterity, that they are capable of doing infinite damage, and as they are made in some of the Frontier towns, where the Indians will procure them at any price, I am of the opinion all white persons should be restricted on a very severe penalty from selling them to the Indians, or for their own use." Source: Documents Relating to the History of Colonial New York, London Documents XXXVII, p. 665. It appears then that Native Americans had some rifles in the 1755 to 1763 time frame, and wanted more, although they also fired "swan shot" in combat. There is a first-person account from the Battle of Lake George during the F and I War that recites a Mohawk running up to about 10 yards and killing an enemy by shooting him in the chest with "a load of swan shot."
In the summer of 1775 a settler on the western frontier near the Mohawk River wrote a letter to the Schenectady Committee of Safety reciting how two Mohawks visiting at his house had warned him that their nation was going to join the British and kill Americans. When a neighbor was seen passing the house on a wagon, one of the Mohawks "lifted his rifle" and declared that he could shoot that man through his left eye. The letter, a copy of which I've seen, specifies "rifle", not "musket". Rifles were still in Native American hands a good ten years after Johnson argued they should be banned from owing them.