That is a video from Lee Nuttall. He is a member here on MFK called "nutty." I believe he collects all his rock and wood locally from rivers and surrounding area. Rocks aren't hard to find, just go outside and look.
I would look at landscape supply stores.
Might be a bit costly in Hawaii, with having to ship it all.
You might consider some form of lava rock/coral, which you should have allot of.
I would use a LFS as the last place to look.
In our area, the landscape stores have a great selection, for not much money.
Good luck