1. Buy a patio broom. Endure the strange looks you will get in the hardware shop as you gaze closely at the bristles of different brooms, checking them for scale thickness. I bought this one at a local IGA.
2. Inform all your family members that the broom you bring home is absolutely not to be used for sweeping as it is a valuable hobby resource. Rise above the satirical comments directed your way.
3. 'Harvest' the bristles as you need them.
4. Gently squeeze the end of the bristle flat, using flat pliers or suchlike.
5. Use a hobby knife to cut the flattened end into the desired shape.
That's it. You now have a massive supply of flexible plastic rods that can be easily transformed into spears, pikes, arrows, even swords etc with a little care, and they have cost you next to nothing.