well to be honest this is not proper way to do it i know but i do not have nerve to play with obsidian or flint carving etc. if you do not such a nerve too, here how i make them...
material needed:
1. polyester and its hardener (i guess epoxy may work too)
2. glass powder
3. arrow point mold
mix the polyester and hardener (hardener is needed 1-3% for polyester) and add enough amount of glass power. the mixture should be like honey fluidity. i tried with glass powder and calcite (marble dust). both seems work but i found glass powder more efficient.
pour the mixture to mold and wait for curing.
once you take out from mold, you need to make some work, like sharpening, shaping the details etc. and then make an arrow.
here is the results: