Flint is a mineral; it is a sedimentary cryptocrystalline form of the mineral quartz.
Biomineralization is a naturally occurring trait of living organisms, and this is process is how seashells get formed, for example.
So, yes, your dragon is some biological manner have a “tongue of flint.” Maybe its tongue has surface that scales flint and regenerates dead tongue skin cells. Maybe your dragon’s mouth is a nice environment for the bacteria similar to the sea floor and it’s that bacteria which produces the mineralization process, which catalyzes on your dragon’s tongue.
Biological production of steel is a bit tougher nut to crack. It doesn’t occur.
But it doesn’t need to occur. I get that you’re going after a literal “flint and steel” fire starting mechanism. But the purpose of the steel in a flint and steel kit is merely to serve as a (relatively softer) material for striking the harder flint against. It is but one, relatively later, materials used to manufacture a class of tools generally called a fire striker within the class of fire starting generally termed “percussion fire making.”
Percussion fire making involve the striking of one material against the other to cleave a small, hot, oxidizing metal particle that can ignite tinder. This contrasts other fire making methods such as volcanic ignition, meteorite strike, lightening, or friction (hand bow, etc.)
Early fire strikers, and fire making, predate the Iron Age and therefore steel. Early fire strikers were manufactured from a variety of iron pyrite. Also marcasite was used with flint and other stones to produce a high-temperature spark that could be used to create fire. For example, anthropologists believe that the "Iceman" called Ötzi may have used iron pyrite to make fire.
Marcasite, sometimes called “white iron pyrite”, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure.
It is a mineral, and that gets us back to mineralization. Or perhaps naturally produced teeth.
However, I would be apt to swap the two: the teeth should be the harder of the flint-and-steel mechanism, perhaps wearing somewhat over time. The tongue should be the sacrificial element, flaking off dead skin cells in the form of sparks that simply get regenerated over night.
Well, that’s how I see it anyway.