Bamboo
Bamboo has a long history of use as a core for Amtgard weapons.
While it may not be as popular as some other cores for swords, it still makes a quite serviceable core, lighter than PVC but not as light as golf club shafts.
It really shines, and is by far the most commonly used core, however, for polearms.
Care must be taken to ensure that thick enough bamboo is used for the length of polearm... what works for a 6' shortspear will not work for a big 15-footer. It should not bend, and even so may be more prone to snapping than other cores if not careful. Remember bamboo should be courtesy padded as required by the Rulebook.
There are many different species of Bamboo, which grow in a wide variety of climates, but the types most used by Amtgard are generally of the "yellow" variety, such as Golden Hawaiian. If you live in an area where appropriate Bamboo grows locally, you may be able to harvest some or grow your own in your backyard. Make sure you find out if it is okay before cutting, just because it is on the side of a road doesn't mean you can just take it.
That being said, even if you can cut it, you can't just use it fresh-cut. Bamboo needs to be properly dried, either by leaving to dry out in a dry place or using some kind of oven or torch. The former method, while easier (any garage should do) will take time... as much as 6 months depending on local humidity.
Bamboo can also be store-bought, or ordered through distributors. Landscaping firms are worth checking into. Home Depot typically sells bamboo fence-sticks, but they are only useful for the shortest spears, usually they are in the 1cm diameter range.
- insert list of bamboo distributors here
Check out the Amtgard Resources page for more information.