Many years ago, a pistol turned up in the area of Fort Ross in California. It appears that it may have been rebuilt some over the centuries, perhaps, and I believe that it is shown in Worman and Garavaglia's two vol. set on Guns of the Early West. It is identified as being Russian, and the fort was built by them. Not sure where the gun is today, but it would be interesting to see it. That is the only one that has come to my attention. It was flintlock and doesn't look like the run of the mill Euro guns. I am sure that there are others out there. The Spanish liklely did not trade guns since an armed population might resist them. As the Russians were also somewhat harsh toward the Indians, they may have held back on letting them have arms, too. Good inquiry; maybe someone here has some information.
Dick