I think the term "Fur Trade" needs some clarification. There was the fur trade era, almost over by the time that the classic Hawken came into it's glory. The Hawken, from the most logical research seems to have been more of an early plains rifle, and Sam stated in an interview in his later years that he made lots for the gold rush. Besides all that, I would be perfectly willing to make an educated guess that a trade gun was more common than most rifles, they were literally made by the boat loads and imported and copied by most of the larger arms makers here. Mariano Medina's powder horn that is documented is cow horn or the straightest buff horn ever. The 1851 drawing of Edwin Denig's Hawken and horn illustrates a horn that is most definitely cow horn shaped. I've yet to find an illustration of any horn owned by Jim Bridger or Kit Carson. While I don't have numbers on how many of each type of original horns are extant, but from the looks of it there are lots more cow that buffalo, and I mean lots.
Now there is the term "For the trade" which were items made as economically as possible to be sold/traded to everyday men and natives. These are the items that the run of the mill frontiersman would have and put to hard usage, and they were normally plain as a plank.