As sort of a secondary question, did native americans ever show much interest in acquiring other european weapons such as swords or polearms? I know Bernal Diaz mentioned Aztecs tying captured Spanish swords to the end of long poles during the retreat from Tenochtitlan, but that's about it.
I'll offer a bit on the firearms part of the question:
The short answer is: The number of muskets used by the Native Americans increased very rapidly in the 1660s - 1690s such that by 1700, practically all native tribes were fully equipped with firearms.
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Among the woodland tribes of what would become the Eastern United States, the musket was needed as much for hunting as it was for war. This meant that the natives would actually refuse to trade for the cumbersome matchlock muskets of the 16th and first half of the 17th centuries, which were wholly inadequate for the task because of their weight and the need to keep the matchcord lit. However, the flintlock musket became common in the late 1600s and the Native Americans saw its effectiveness demonstrated by traders or settlers going out to hunt. The lesser weight and greater reliability of flintlock weapons made them capable of being used for that important hunting role, and they were much more powerful, accurate, and longer ranged than the short hunting bows that the woodland indians had used prior to them.
The tribes never developed enough understanding of chemistry or metallurgy to maintain their muskets or create large quantities of gunpowder, and as such, were forced to court one of the European empires in order to maintain their local supply. And since arms manufacturing was strictly prohibited in the colonies, they had to go to agents and traders who were supplied by royal arms manufacturers in Europe. For their part, the crowns of Europe officially banned the musket as a trade good at various times, but the major powers (France, England, and to a lesser extent, Spain) realized that guns and ammunition were a convenient trade: they made the tribes more closely allied militarily, better able to fight, and more reliant on their trading partner.
Geopolitics overrode the desire to prevent the natives from having weapons they could use to raid friendly settlements. The European monarchs did not want to commit large numbers of troops to the North American frontier - their strength was needed for the seemingly never ending succession of wars on the European continent. (It turned out that they had a hard time fighting in the woods anyway). So they instead courted the native tribes in order to keep the peace on their frontiers and try to put pressure on their rivals.
The natural result was thus that as long as there were opposing sides, the tribes would be well equipped with firearms.