I did not really read the posts above, but. If you want to make plugs, i suggest using wood. Bone would also work but that shit cant be rough, and a six is pretty small, i dont know how easy id be to make such small plugs being they would be so delicate.
If you do decided to make some out of wood, you want to use a hard wood, not soft wood like pine. Walnut works good, and those trees are pretty easy to find/ identify at least in my area (Michigan).
Here are a few pair of plugs i hand carved from walnut, they still needed sanding:
And here is some bamboo i am drying out. You can use bamboo, its a nice hard wood, not to mention easy to cut. Only thing is bamboo drying can be really hard, you have to dry it a certain way or it will crack, its very detailed and probably not worth it.
Most people who craft plugs use a lathe or wood turning machine, which can cost anywhere from $200-$5,000. Just google organic plugs or organic jewelry.
I suggest maybe looking around this website:
ORGANIC: Natural Body Jewelry
Hope this helps.