Instead of obsidian, why not practice with regular glass? I read an article in Backwoodsman where the author used the round bottoms of glass bottles to make points from. They looked pretty nice. Another article used old toilet porcelain. You can use nails for pressure flaking.
Around 1861 they ran the first telegraph line across the great plains and put the Pony Express out of business. The Indians soon discovered the glass insulators through which the telegraph line ran. They were great. Easy to find. Easy to knap. New blades on demand. Pilfered insulation became such a maintenance problem that Western Union took to putting piles of glass at the foot of the poles. As long as the Indians could find material for arrowheads without climbing for them, the insulators were safe.
