This post has me curious about something...were there any other kinds of materials were used when flints weren't available to get a spark in a flintlock?
These would be emergency situations, purely anecdotal. It's probably unlikely, too, given that in North America the Natuves had spread flint throughout the continent by using trade networks where it didn't occur naturally. Euro-American settlers found a lot everywhere. For example, Joseph Doddroge states that in Western Pennsylvania in the 1770s people found arrowheads that they used in their guns.
Wondering if there was a preferred material in a pinch